Until more flags for kvm_run.emulation_failure flags are defined, it
is undetermined whether new payload elements corresponding to those
flags will be additive or alternative. As a hint to userspace that an
alternative is possible, wrap the current payload elements in a union.
Suggested-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NDavid Edmondson <david.edmondson@oracle.com>
Reviewed-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210920103737.2696756-2-david.edmondson@oracle.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Though gcc conveniently compiles a simple memset to "rep stos," clang
prefers to call the libc version of memset. If a test is dynamically
linked, the libc memset isn't available in L1 (nor is the PLT or the
GOT, for that matter). Even if the test is statically linked, the libc
memset may choose to use some CPU features, like AVX, which may not be
enabled in L1. Note that __builtin_memset doesn't solve the problem,
because (a) the compiler is free to call memset anyway, and (b)
__builtin_memset may also choose to use features like AVX, which may
not be available in L1.

To avoid a myriad of problems, use an explicit "rep stos" to clear the
VMCB in generic_svm_setup(), which is called both from L0 and L1.
Reported-by: NRicardo Koller <ricarkol@google.com>
Signed-off-by: NJim Mattson <jmattson@google.com>
Fixes: 20ba262f ("selftests: KVM: AMD Nested test infrastructure")
Message-Id: <20210930003649.4026553-1-jmattson@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This variable was renamed to kvm_has_noapic_vcpu in commit
6e4e3b4d ("KVM: Stop using deprecated jump label APIs").
Signed-off-by: NJim Mattson <jmattson@google.com>
Message-Id: <20211021185449.3471763-1-jmattson@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Unregister KVM's posted interrupt wakeup handler during unsetup so that a
spurious interrupt that arrives after kvm_intel.ko is unloaded doesn't
call into freed memory.

Fixes: bf9f6ac8 ("KVM: Update Posted-Interrupts Descriptor when vCPU is blocked")
Cc: stable@vger.kernel.org
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211009001107.3936588-3-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Add a synchronize_rcu() after clearing the posted interrupt wakeup handler
to ensure all readers, i.e. in-flight IRQ handlers, see the new handler
before returning to the caller.  If the caller is an exiting module and
is unregistering its handler, failure to wait could result in the IRQ
handler jumping into an unloaded module.

The registration path doesn't require synchronization, as it's the
caller's responsibility to not generate interrupts it cares about until
after its handler is registered.

Fixes: f6b3c72c ("x86/irq: Define a global vector for VT-d Posted-Interrupts")
Cc: stable@vger.kernel.org
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211009001107.3936588-2-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Use a rw_semaphore instead of a mutex to coordinate APICv updates so that
vCPUs responding to requests can take the lock for read and run in
parallel.  Using a mutex forces serialization of vCPUs even though
kvm_vcpu_update_apicv() only touches data local to that vCPU or is
protected by a different lock, e.g. SVM's ir_list_lock.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211022004927.1448382-5-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Move SVM's assertion that vCPU's APICv state is consistent with its VM's
state out of svm_vcpu_run() and into x86's common inner run loop.  The
assertion and underlying logic is not unique to SVM, it's just that SVM
has more inhibiting conditions and thus is more likely to run headfirst
into any KVM bugs.

Add relevant comments to document exactly why the update path has unusual
ordering between the update the kick, why said ordering is safe, and also
the basic rules behind the assertion in the run loop.

Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211022004927.1448382-3-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Commit 99cdc6c1 ("RISC-V: Add initial skeletal KVM support") selects
the config ANON_INODES in config KVM, but the config ANON_INODES is removed
since commit 5dd50aae ("Make anon_inodes unconditional") in 2018.

Hence, ./scripts/checkkconfigsymbols.py warns on non-existing symbols:

  ANON_INODES
  Referencing files: arch/riscv/kvm/Kconfig

Remove selecting the non-existing config ANON_INODES.
Signed-off-by: NLukas Bulwahn <lukas.bulwahn@gmail.com>
Message-Id: <20211022061514.25946-1-lukas.bulwahn@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Extract the zapping of rmaps, a.k.a. legacy MMU, for a gfn range to a
separate helper to clean up the unholy mess that kvm_zap_gfn_range() has
become.  In addition to deep nesting, the rmaps zapping spreads out the
declaration of several variables and is generally a mess.  Clean up the
mess now so that future work to improve the memslots implementation
doesn't need to deal with it.

Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211022010005.1454978-4-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Remove an unnecessary remote TLB flush in kvm_zap_gfn_range() now that
said function holds mmu_lock for write for its entire duration.  The
flush was added by the now-reverted commit to allow TDP MMU to flush while
holding mmu_lock for read, as the transition from write=>read required
dropping the lock and thus a pending flush needed to be serviced.

Fixes: 5a324c24 ("Revert "KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock"")
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211022010005.1454978-3-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

A recent commit to fix the calls to kvm_flush_remote_tlbs_with_address()
in kvm_zap_gfn_range() inadvertantly added yet another flush instead of
fixing the existing flush.  Drop the redundant flush, and fix the params
for the existing flush.

Cc: stable@vger.kernel.org
Fixes: 2822da44 ("KVM: x86/mmu: fix parameters to kvm_flush_remote_tlbs_with_address")
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211022010005.1454978-2-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

kvm_mmu_unload() destroys all the PGD caches.  Use the lighter
kvm_mmu_sync_roots() and kvm_mmu_sync_prev_roots() instead.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211019110154.4091-5-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The commit 578e1c4d ("kvm: x86: Avoid taking MMU lock
in kvm_mmu_sync_roots if no sync is needed") added smp_wmb() in
mmu_try_to_unsync_pages(), but the corresponding smp_load_acquire() isn't
used on the load of SPTE.W.  smp_load_acquire() orders _subsequent_
loads after sp->is_unsync; it does not order _earlier_ loads before
the load of sp->is_unsync.

This has no functional change; smp_rmb() is a NOP on x86, and no
compiler barrier is required because there is a VMEXIT between the
load of SPTE.W and kvm_mmu_snc_roots.

Cc: Junaid Shahid <junaids@google.com>
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211019110154.4091-4-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The commit 21823fbd ("KVM: x86: Invalidate all PGDs for the
current PCID on MOV CR3 w/ flush") invalidates all PGDs for the specific
PCID and in the case of PCID is disabled, it includes all PGDs in the
prev_roots and the commit made prev_roots totally unused in this case.

Not using prev_roots fixes a problem when CR4.PCIDE is changed 0 -> 1
before the said commit:

	(CR4.PCIDE=0, CR4.PGE=1; CR3=cr3_a; the page for the guest
	 RIP is global; cr3_b is cached in prev_roots)

	modify page tables under cr3_b
		the shadow root of cr3_b is unsync in kvm
	INVPCID single context
		the guest expects the TLB is clean for PCID=0
	change CR4.PCIDE 0 -> 1
	switch to cr3_b with PCID=0,NOFLUSH=1
		No sync in kvm, cr3_b is still unsync in kvm
	jump to the page that was modified in step 1
		shadow page tables point to the wrong page

It is a very unlikely case, but it shows that stale prev_roots can be
a problem after CR4.PCIDE changes from 0 to 1.  However, to fix this
case, the commit disabled caching CR3 in prev_roots altogether when PCID
is disabled.  Not all CPUs have PCID; especially the PCID support
for AMD CPUs is kind of recent.  To restore the prev_roots optimization
for CR4.PCIDE=0, flush the whole MMU (including all prev_roots) when
CR4.PCIDE changes.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211019110154.4091-3-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The KVM doesn't know whether any TLB for a specific pcid is cached in
the CPU when tdp is enabled.  So it is better to flush all the guest
TLB when invalidating any single PCID context.

The case is very rare or even impossible since KVM generally doesn't
intercept CR3 write or INVPCID instructions when tdp is enabled, so the
fix is mostly for the sake of overall robustness.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211019110154.4091-2-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

X86_CR4_PGE doesn't participate in kvm_mmu_role, so the mmu context
doesn't need to be reset.  It is only required to flush all the guest
tlb.

It is also inconsistent that X86_CR4_PGE is in KVM_MMU_CR4_ROLE_BITS
while kvm_mmu_role doesn't use X86_CR4_PGE.  So X86_CR4_PGE is also
removed from KVM_MMU_CR4_ROLE_BITS.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Reviewed-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210919024246.89230-3-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

X86_CR4_PCIDE doesn't participate in kvm_mmu_role, so the mmu context
doesn't need to be reset.  It is only required to flush all the guest
tlb.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Reviewed-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210919024246.89230-2-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Recent kernels have checks to ensure the GPA values in special-purpose
registers like CR3 are within the maximum physical address range and
don't overlap with anything in the upper/reserved range. In the case of
SEV kselftest guests booting directly into 64-bit mode, CR3 needs to be
initialized to the GPA of the page table root, with the encryption bit
set. The kernel accounts for this encryption bit by removing it from
reserved bit range when the guest advertises the bit position via
KVM_SET_CPUID*, but kselftests currently call KVM_SET_SREGS as part of
vm_vcpu_add_default(), before KVM_SET_CPUID*.

As a result, KVM_SET_SREGS will return an error in these cases.
Address this by moving vcpu_set_cpuid() (which calls KVM_SET_CPUID*)
ahead of vcpu_setup() (which calls KVM_SET_SREGS).

While there, address a typo in the assertion that triggers when
KVM_SET_SREGS fails.
Suggested-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NMichael Roth <michael.roth@amd.com>
Message-Id: <20211006203617.13045-1-michael.roth@amd.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NNathan Tempelman <natet@google.com>

SDM mentioned that, RDPMC:

  IF (((CR4.PCE = 1) or (CPL = 0) or (CR0.PE = 0)) and (ECX indicates a supported counter))
      THEN
          EAX := counter[31:0];
          EDX := ZeroExtend(counter[MSCB:32]);
      ELSE (* ECX is not valid or CR4.PCE is 0 and CPL is 1, 2, or 3 and CR0.PE is 1 *)
          #GP(0);
  FI;

Let's add a comment why CR0.PE isn't tested since it's impossible for CPL to be >0 if
CR0.PE=0.
Signed-off-by: NWanpeng Li <wanpengli@tencent.com>
Message-Id: <1634724836-73721-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Paul pointed out the error messages when KVM fails to load are unhelpful
in understanding exactly what went wrong if userspace probes the "wrong"
module.

Add a mandatory kvm_x86_ops field to track vendor module names, kvm_intel
and kvm_amd, and use the name for relevant error message when KVM fails
to load so that the user knows which module failed to load.

Opportunistically tweak the "disabled by bios" error message to clarify
that _support_ was disabled, not that the module itself was magically
disabled by BIOS.
Suggested-by: NPaul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20211018183929.897461-2-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Currently, the NX huge page recovery thread wakes up every minute and
zaps 1/nx_huge_pages_recovery_ratio of the total number of split NX
huge pages at a time. This is intended to ensure that only a
relatively small number of pages get zapped at a time. But for very
large VMs (or more specifically, VMs with a large number of
executable pages), a period of 1 minute could still result in this
number being too high (unless the ratio is changed significantly,
but that can result in split pages lingering on for too long).

This change makes the period configurable instead of fixing it at
1 minute. Users of large VMs can then adjust the period and/or the
ratio to reduce the number of pages zapped at one time while still
maintaining the same overall duration for cycling through the
entire list. By default, KVM derives a period from the ratio such
that a page will remain on the list for 1 hour on average.
Signed-off-by: NJunaid Shahid <junaids@google.com>
Message-Id: <20211020010627.305925-1-junaids@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

SDM section 18.2.3 mentioned that:

  "IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
   any general-purpose or fixed-function counters via a single WRMSR."

It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
the value is always 0 for ICX/SKX boxes on hands. Let's fill get_msr
MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior and drop
global_ovf_ctrl variable.
Tested-by: NLike Xu <likexu@tencent.com>
Signed-off-by: NWanpeng Li <wanpengli@tencent.com>
Message-Id: <1634631160-67276-2-git-send-email-wanpengli@tencent.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

slot_handle_leaf is a misnomer because it only operates on 4K SPTEs
whereas "leaf" is used to describe any valid terminal SPTE (4K or
large page). Rename slot_handle_leaf to slot_handle_level_4k to
avoid confusion.

Making this change makes it more obvious there is a benign discrepency
between the legacy MMU and the TDP MMU when it comes to dirty logging.
The legacy MMU only iterates through 4K SPTEs when zapping for
collapsing and when clearing D-bits. The TDP MMU, on the other hand,
iterates through SPTEs on all levels.

The TDP MMU behavior of zapping SPTEs at all levels is technically
overkill for its current dirty logging implementation, which always
demotes to 4k SPTES, but both the TDP MMU and legacy MMU zap if and only
if the SPTE can be replaced by a larger page, i.e. will not spuriously
zap 2m (or larger) SPTEs. Opportunistically add comments to explain this
discrepency in the code.
Signed-off-by: NDavid Matlack <dmatlack@google.com>
Message-Id: <20211019162223.3935109-1-dmatlack@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Per Intel SDM, RTIT_CTL_BRANCH_EN bit has no dependency on any CPUID
leaf 0x14.
Signed-off-by: NXiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20210827070249.924633-5-xiaoyao.li@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

To better self explain the meaning of this field and match the
PT_CAP_num_address_ranges constatn.
Suggested-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NXiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20210827070249.924633-4-xiaoyao.li@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The number of valid PT ADDR MSRs for the guest is precomputed in
vmx->pt_desc.addr_range. Use it instead of calculating again.
Signed-off-by: NXiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20210827070249.924633-3-xiaoyao.li@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

A minor optimization to WRMSR MSR_IA32_RTIT_CTL when necessary.

Opportunistically refine the comment to call out that KVM requires
VM_EXIT_CLEAR_IA32_RTIT_CTL to expose PT to the guest.
Reviewed-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NXiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20210827070249.924633-2-xiaoyao.li@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

"prefetch", "prefault" and "speculative" are used throughout KVM to mean
the same thing.  Use a single name, standardizing on "prefetch" which
is already used by various functions such as direct_pte_prefetch,
FNAME(prefetch_gpte), FNAME(pte_prefetch), etc.
Suggested-by: NDavid Matlack <dmatlack@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Unify the flags for rmaps and page tracking data, using a
single flag in struct kvm_arch and a single loop to go
over all the address spaces and memslots.  This avoids
code duplication between alloc_all_memslots_rmaps and
kvm_page_track_enable_mmu_write_tracking.
Signed-off-by: NDavid Stevens <stevensd@chromium.org>
[This patch is the delta between David's v2 and v3, with conflicts
 fixed and my own commit message. - Paolo]
Co-developed-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Introduce a KVM selftest to verify that userspace manipulation of the
TSC (via the new vCPU attribute) results in the correct behavior within
the guest.
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181555.973085-6-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

vCPU file descriptors are abstracted away from test code in KVM
selftests, meaning that tests cannot directly access a vCPU's device
attributes. Add helpers that tests can use to get at vCPU device
attributes.
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181555.973085-5-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

The KVM_CREATE_DEVICE and KVM_{GET,SET}_DEVICE_ATTR ioctls are defined
to return a value of zero on success. As such, tighten the assertions in
the helper functions to only pass if the return code is zero.
Suggested-by: NAndrew Jones <drjones@redhat.com>
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181555.973085-4-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Add a selftest for the new KVM clock UAPI that was introduced. Ensure
that the KVM clock is consistent between userspace and the guest, and
that the difference in realtime will only ever cause the KVM clock to
advance forward.

Cc: Andrew Jones <drjones@redhat.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181555.973085-3-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Copy over approximately clean versions of the pvclock headers into
tools. Reconcile headers/symbols missing in tools that are unneeded.
Signed-off-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181555.973085-2-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

To date, VMM-directed TSC synchronization and migration has been a bit
messy. KVM has some baked-in heuristics around TSC writes to infer if
the VMM is attempting to synchronize. This is problematic, as it depends
on host userspace writing to the guest's TSC within 1 second of the last
write.

A much cleaner approach to configuring the guest's views of the TSC is to
simply migrate the TSC offset for every vCPU. Offsets are idempotent,
and thus not subject to change depending on when the VMM actually
reads/writes values from/to KVM. The VMM can then read the TSC once with
KVM_GET_CLOCK to capture a (realtime, host_tsc) pair at the instant when
the guest is paused.

Cc: David Matlack <dmatlack@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210916181538.968978-8-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Refactor kvm_synchronize_tsc to make a new function that allows callers
to specify TSC parameters (offset, value, nanoseconds, etc.) explicitly
for the sake of participating in TSC synchronization.
Signed-off-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181538.968978-7-oupton@google.com>
[Make sure kvm->arch.cur_tsc_generation and vcpu->arch.this_tsc_generation are
 equal at the end of __kvm_synchronize_tsc, if matched is false. Reported by
 Maxim Levitsky. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Protect the reference point for kvmclock with a seqcount, so that
kvmclock updates for all vCPUs can proceed in parallel.  Xen runstate
updates will also run in parallel and not bounce the kvmclock cacheline.

Of the variables that were protected by pvclock_gtod_sync_lock,
nr_vcpus_matched_tsc is different because it is updated outside
pvclock_update_vm_gtod_copy and read inside it.  Therefore, we
need to keep it protected by a spinlock.  In fact it must now
be a raw spinlock, because pvclock_update_vm_gtod_copy, being the
write-side of a seqcount, is non-preemptible.  Since we already
have tsc_write_lock which is a raw spinlock, we can just use
tsc_write_lock as the lock that protects the write-side of the
seqcount.
Co-developed-by: NOliver Upton <oupton@google.com>
Message-Id: <20210916181538.968978-6-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Handling the migration of TSCs correctly is difficult, in part because
Linux does not provide userspace with the ability to retrieve a (TSC,
realtime) clock pair for a single instant in time. In lieu of a more
convenient facility, KVM can report similar information in the kvm_clock
structure.

Provide userspace with a host TSC & realtime pair iff the realtime clock
is based on the TSC. If userspace provides KVM_SET_CLOCK with a valid
realtime value, advance the KVM clock by the amount of elapsed time. Do
not step the KVM clock backwards, though, as it is a monotonic
oscillator.
Suggested-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210916181538.968978-5-oupton@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This is a new warning in clang top-of-tree (will be clang 14):

In file included from arch/x86/kvm/mmu/mmu.c:27:
arch/x86/kvm/mmu/spte.h:318:9: error: use of bitwise '|' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
        return __is_bad_mt_xwr(rsvd_check, spte) |
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                                 ||
arch/x86/kvm/mmu/spte.h:318:9: note: cast one or both operands to int to silence this warning

The code is fine, but change it anyway to shut up this clever clogs
of a compiler.

Reported-by: torvic9@mailbox.org
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>