This was tested by booting a nested guest with TSC=1Ghz,
observing the clocks, and doing about 100 cycles of migration.

Note that qemu patch is needed to support migration because
of a new MSR that needs to be placed in the migration state.

The patch will be sent to the qemu mailing list soon.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210914154825.104886-14-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This allows to easily simulate a CPU without this feature.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210914154825.104886-13-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Commit adc2a237 ("KVM: nSVM: improve SYSENTER emulation on AMD"),
made init_vmcb set vmload/vmsave intercepts unconditionally,
and relied on svm_vcpu_after_set_cpuid to clear them when possible.

However init_vmcb is also called when the vCPU is reset, and it is
not followed by another call to svm_vcpu_after_set_cpuid because
the CPUID is already set.  This mistake makes the VMSAVE/VMLOAD intercept
to be set when it is not needed, and harms performance of the nested
guest.

Extract the relevant parts of svm_vcpu_after_set_cpuid so that they
can be called again on reset.

Fixes: adc2a237 ("KVM: nSVM: improve SYSENTER emulation on AMD")
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

This is useful for debug and also makes it consistent with
the rest of the SVM optional features.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210914154825.104886-9-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Move RESET emulation for SVM vCPUs to svm_vcpu_reset(), and drop an extra
init_vmcb() from svm_create_vcpu() in the process.  Hopefully KVM will
someday expose a dedicated RESET ioctl(), and in the meantime separating
"create" from "RESET" is a nice cleanup.

Keep the call to svm_switch_vmcb() so that misuse of svm->vmcb at worst
breaks the guest, e.g. premature accesses doesn't cause a NULL pointer
dereference.

Cc: Reiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210921000303.400537-10-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

GP SVM errata workaround made the #GP handler always emulate
the SVM instructions.

However these instructions #GP in case the operand is not 4K aligned,
but the workaround code didn't check this and we ended up
emulating these instructions anyway.

This is only an emulation accuracy check bug as there is no harm for
KVM to read/write unaligned vmcb images.

Fixes: 82a11e9c ("KVM: SVM: Add emulation support for #GP triggered by SVM instructions")
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210914154825.104886-4-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

In svm_clear_vintr we try to restore the virtual interrupt
injection that might be pending, but we fail to restore
the interrupt vector.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210914154825.104886-2-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Use return statements instead of nested if, and fix error
path to free all the maps that were allocated.
Suggested-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210913140954.165665-2-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Currently the KVM_REQ_GET_NESTED_STATE_PAGES on SVM only reloads PDPTRs,
and MSR bitmap, with former not really needed for SMM as SMM exit code
reloads them again from SMRAM'S CR3, and later happens to work
since MSR bitmap isn't modified while in SMM.

Still it is better to be consistient with VMX.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210913140954.165665-5-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Otherwise guest entry code might see incorrect L1 state (e.g paging state).

Fixes: 37be407b ("KVM: nSVM: Fix L1 state corruption upon return from SMM")
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210913140954.165665-3-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

When the 5-level page table is enabled on host OS, the nested page table
for guest VMs must use 5-level as well. Update get_npt_level() function
to reflect this requirement. In the meanwhile, remove the code that
prevents kvm-amd driver from being loaded when 5-level page table is
detected.
Signed-off-by: NWei Huang <wei.huang2@amd.com>
Message-Id: <20210818165549.3771014-4-wei.huang2@amd.com>
[Tweak condition as suggested by Sean. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

AMD future CPUs will require a 5-level NPT if host CR4.LA57 is set.
To prevent kvm_mmu_get_tdp_level() from incorrectly changing NPT level
on behalf of CPUs, add a new parameter in kvm_configure_mmu() to force
a fixed TDP level.
Signed-off-by: NWei Huang <wei.huang2@amd.com>
Message-Id: <20210818165549.3771014-2-wei.huang2@amd.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Split the check for having a vmexit handler to svm_check_exit_valid,
and make svm_handle_invalid_exit only handle a vmexit that is
already not valid.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210811122927.900604-2-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

APIC base relocation is not supported anyway and won't work
correctly so just drop the code that handles it and keep AVIC
MMIO bar at the default APIC base.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-17-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

No functional change intended.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-15-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Now that kvm_request_apicv_update doesn't need to drop the kvm->srcu lock,
we can call kvm_request_apicv_update directly.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210810205251.424103-13-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

It is never a good idea to enter a guest on a vCPU when the
AVIC inhibition state doesn't match the enablement of
the AVIC on the vCPU.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-11-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Thanks to the former patches, it is now possible to keep the APICv
memslot always enabled, and it will be invisible to the guest
when it is inhibited

This code is based on a suggestion from Sean Christopherson:
https://lkml.org/lkml/2021/7/19/2970Suggested-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-9-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

* Invert the mask of bits that we pick from L2 in
  nested_vmcb02_prepare_control

* Invert and explicitly use VIRQ related bits bitmask in svm_clear_vintr

This fixes a security issue that allowed a malicious L1 to run L2 with
AVIC enabled, which allowed the L2 to exploit the uninitialized and enabled
AVIC to read/write the host physical memory at some offsets.

Fixes: 3d6368ef ("KVM: SVM: Add VMRUN handler")
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Remove the __kvm_handle_fault_on_reboot() and __ex() macros now that all
VMX and SVM instructions use asm goto to handle the fault (or in the
case of VMREAD, completely custom logic).  Drop kvm_spurious_fault()'s
asmlinkage annotation as __kvm_handle_fault_on_reboot() was the only
flow that invoked it from assembly code.

Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Like Xu <like.xu.linux@gmail.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210809173955.1710866-2-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Drop redundant clears of vcpu->arch.hflags in init_vmcb() since
kvm_vcpu_reset() always clears hflags, and it is also always
zero at vCPU creation time.  And of course, the second clearing
in init_vmcb() was always redundant.
Suggested-by: NReiji Watanabe <reijiw@google.com>
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-46-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Emulate a full #INIT instead of simply initializing the VMCB if the
guest hits a shutdown.  Initializing the VMCB but not other vCPU state,
much of which is mirrored by the VMCB, results in incoherent and broken
vCPU state.

Ideally, KVM would not automatically init anything on shutdown, and
instead put the vCPU into e.g. KVM_MP_STATE_UNINITIALIZED and force
userspace to explicitly INIT or RESET the vCPU.  Even better would be to
add KVM_MP_STATE_SHUTDOWN, since technically NMI can break shutdown
(and SMI on Intel CPUs).

But, that ship has sailed, and emulating #INIT is the next best thing as
that has at least some connection with reality since there exist bare
metal platforms that automatically INIT the CPU if it hits shutdown.

Fixes: 46fe4ddd ("[PATCH] KVM: SVM: Propagate cpu shutdown events to userspace")
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-45-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Move the setting of CR0, CR4, EFER, RFLAGS, and RIP from vendor code to
common x86.  VMX and SVM now have near-identical sequences, the only
difference being that VMX updates the exception bitmap.  Updating the
bitmap on SVM is unnecessary, but benign.  Unfortunately it can't be left
behind in VMX due to the need to update exception intercepts after the
control registers are set.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-37-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Move code to stuff vmcb->save.dr6 to its architectural init value from
svm_vcpu_reset() into sev_es_sync_vmsa().  Except for protected guests,
a.k.a. SEV-ES guests, vmcb->save.dr6 is set during VM-Enter, i.e. the
extra write is unnecessary.  For SEV-ES, stuffing save->dr6 handles a
theoretical case where the VMSA could be encrypted before the first
KVM_RUN.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-33-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Drop direct writes to vmcb->save.cr4 during vCPU RESET/INIT, as the
values being written are fully redundant with respect to
svm_set_cr4(vcpu, 0) a few lines earlier.  Note, svm_set_cr4() also
correctly forces X86_CR4_PAE when NPT is disabled.

No functional change intended.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-32-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Hoist svm_set_cr0() up in the sequence of register initialization during
vCPU RESET/INIT, purely to match VMX so that a future patch can move the
sequences to common x86.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-31-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Drop unnecessary initialization of vmcb->save.rip during vCPU RESET/INIT,
as svm_vcpu_run() unconditionally propagates VCPU_REGS_RIP to save.rip.

No true functional change intended.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-21-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Move the EDX initialization at vCPU RESET, which is now identical between
VMX and SVM, into common code.

No functional change intended.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-20-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Consolidate the APIC base RESET logic, which is currently spread out
across both x86 and vendor code.  For an in-kernel APIC, the vendor code
is redundant.  But for a userspace APIC, KVM relies on the vendor code
to initialize vcpu->arch.apic_base.  Hoist the vcpu->arch.apic_base
initialization above the !apic check so that it applies to both flavors
of APIC emulation, and delete the vendor code.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-19-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Drop an explicit MMU reset in SVM's vCPU RESET/INIT flow now that the
common x86 path correctly handles conditional MMU resets, e.g. if INIT
arrives while the vCPU is in 64-bit mode.

This reverts commit ebae871a ("kvm: svm: reset mmu on VCPU reset").
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-9-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

At vCPU RESET/INIT (mostly RESET), stuff EDX with KVM's hardcoded,
default Family-Model-Stepping ID of 0x600 if CPUID.0x1 isn't defined.
At RESET, the CPUID lookup is guaranteed to "miss" because KVM emulates
RESET before exposing the vCPU to userspace, i.e. userspace can't
possibly have done set the vCPU's CPUID model, and thus KVM will always
write '0'.  At INIT, using 0x600 is less bad than using '0'.

While initializing EDX to '0' is _extremely_ unlikely to be noticed by
the guest, let alone break the guest, and can be overridden by
userspace for the RESET case, using 0x600 is preferable as it will allow
consolidating the relevant VMX and SVM RESET/INIT logic in the future.
And, digging through old specs suggests that neither Intel nor AMD have
ever shipped a CPU that initialized EDX to '0' at RESET.

Regarding 0x600 as KVM's default Family, it is a sane default and in
many ways the most appropriate.  Prior to the 386 implementations, DX
was undefined at RESET.  With the 386, 486, 586/P5, and 686/P6/Athlon,
both Intel and AMD set EDX to 3, 4, 5, and 6 respectively.  AMD switched
to using '15' as its primary Family with the introduction of AMD64, but
Intel has continued using '6' for the last few decades.

So, '6' is a valid Family for both Intel and AMD CPUs, is compatible
with both 32-bit and 64-bit CPUs (albeit not a perfect fit for 64-bit
AMD), and of the common Families (3 - 6), is the best fit with respect to
KVM's virtual CPU model.  E.g. prior to the P6, Intel CPUs did not have a
STI window.  Modern operating systems, Linux included, rely on the STI
window, e.g. for "safe halt", and KVM unconditionally assumes the virtual
CPU has an STI window.  Thus enumerating a Family ID of 3, 4, or 5 would
be provably wrong.

Opportunistically remove a stale comment.

Fixes: 66f7b72e ("KVM: x86: Make register state after reset conform to specification")
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-7-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Do not allow an inexact CPUID "match" when querying the guest's CPUID.0x1
to stuff EDX during INIT.  In the common case, where the guest CPU model
is an AMD variant, allowing an inexact match is a nop since KVM doesn't
emulate Intel's goofy "out-of-range" logic for AMD and Hygon.  If the
vCPU model happens to be an Intel variant, an inexact match is possible
if and only if the max CPUID leaf is precisely '0'. Aside from the fact
that there's probably no CPU in existence with a single CPUID leaf, if
the max CPUID leaf is '0', that means that CPUID.0.EAX is '0', and thus
an inexact match for CPUID.0x1.EAX will also yield '0'.

So, with lots of twisty logic, no functional change intended.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-6-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Explicitly set GDTR.base and IDTR.base to zero when intializing the VMCB.
Functionally this only affects INIT, as the bases are implicitly set to
zero on RESET by virtue of the VMCB being zero allocated.

Per AMD's APM, GDTR.base and IDTR.base are zeroed after RESET and INIT.

Fixes: 04d2cc77 ("KVM: Move main vcpu loop into subarch independent code")
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-4-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: NIsaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Message-Id: <0e8760a26151f47dc47052b25ca8b84fffe0641e.1625186503.git.isaku.yamahata@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

It is possible for AVIC inhibit and AVIC active state to be mismatched.
Currently we disable AVIC right away on vCPU which started the AVIC inhibit
request thus this warning doesn't trigger but at least in theory,
if svm_set_vintr is called at the same time on multiple vCPUs,
the warning can happen.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210713142023.106183-2-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Right now, svm_hv_vmcb_dirty_nested_enlightenments has an incorrect
dereference of vmcb->control.reserved_sw before the vmcb is checked
for being non-NULL.  The compiler is usually sinking the dereference
after the check; instead of doing this ourselves in the source,
ensure that svm_hv_vmcb_dirty_nested_enlightenments is only called
with a non-NULL VMCB.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Cc: Vineeth Pillai <viremana@linux.microsoft.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
[Untested for now due to issues with my AMD machine. - Paolo]

Make svm_copy_vmrun_state()/svm_copy_vmloadsave_state() interface match
'memcpy(dest, src)' to avoid any confusion.

No functional change intended.
Suggested-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210719090322.625277-1-vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

To match svm_copy_vmrun_state(), rename nested_svm_vmloadsave() to
svm_copy_vmloadsave_state().

Opportunistically add missing braces to 'else' branch in
vmload_vmsave_interception().

No functional change intended.
Suggested-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210716144104.465269-1-vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

If the VM was migrated while in SMM, no nested state was saved/restored,
and therefore svm_leave_smm has to load both save and control area
of the vmcb12. Save area is already loaded from HSAVE area,
so now load the control area as well from the vmcb12.
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210628104425.391276-6-vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

VMCB split commit 4995a368 ("KVM: SVM: Use a separate vmcb for the
nested L2 guest") broke return from SMM when we entered there from guest
(L2) mode. Gen2 WS2016/Hyper-V is known to do this on boot. The problem
manifests itself like this:

  kvm_exit:             reason EXIT_RSM rip 0x7ffbb280 info 0 0
  kvm_emulate_insn:     0:7ffbb280: 0f aa
  kvm_smm_transition:   vcpu 0: leaving SMM, smbase 0x7ffb3000
  kvm_nested_vmrun:     rip: 0x000000007ffbb280 vmcb: 0x0000000008224000
    nrip: 0xffffffffffbbe119 int_ctl: 0x01020000 event_inj: 0x00000000
    npt: on
  kvm_nested_intercepts: cr_read: 0000 cr_write: 0010 excp: 40060002
    intercepts: fd44bfeb 0000217f 00000000
  kvm_entry:            vcpu 0, rip 0xffffffffffbbe119
  kvm_exit:             reason EXIT_NPF rip 0xffffffffffbbe119 info
    200000006 1ab000
  kvm_nested_vmexit:    vcpu 0 reason npf rip 0xffffffffffbbe119 info1
    0x0000000200000006 info2 0x00000000001ab000 intr_info 0x00000000
    error_code 0x00000000
  kvm_page_fault:       address 1ab000 error_code 6
  kvm_nested_vmexit_inject: reason EXIT_NPF info1 200000006 info2 1ab000
    int_info 0 int_info_err 0
  kvm_entry:            vcpu 0, rip 0x7ffbb280
  kvm_exit:             reason EXIT_EXCP_GP rip 0x7ffbb280 info 0 0
  kvm_emulate_insn:     0:7ffbb280: 0f aa
  kvm_inj_exception:    #GP (0x0)

Note: return to L2 succeeded but upon first exit to L1 its RIP points to
'RSM' instruction but we're not in SMM.

The problem appears to be that VMCB01 gets irreversibly destroyed during
SMM execution. Previously, we used to have 'hsave' VMCB where regular
(pre-SMM) L1's state was saved upon nested_svm_vmexit() but now we just
switch to VMCB01 from VMCB02.

Pre-split (working) flow looked like:
- SMM is triggered during L2's execution
- L2's state is pushed to SMRAM
- nested_svm_vmexit() restores L1's state from 'hsave'
- SMM -> RSM
- enter_svm_guest_mode() switches to L2 but keeps 'hsave' intact so we have
  pre-SMM (and pre L2 VMRUN) L1's state there
- L2's state is restored from SMRAM
- upon first exit L1's state is restored from L1.

This was always broken with regards to svm_get_nested_state()/
svm_set_nested_state(): 'hsave' was never a part of what's being
save and restored so migration happening during SMM triggered from L2 would
never restore L1's state correctly.

Post-split flow (broken) looks like:
- SMM is triggered during L2's execution
- L2's state is pushed to SMRAM
- nested_svm_vmexit() switches to VMCB01 from VMCB02
- SMM -> RSM
- enter_svm_guest_mode() switches from VMCB01 to VMCB02 but pre-SMM VMCB01
  is already lost.
- L2's state is restored from SMRAM
- upon first exit L1's state is restored from VMCB01 but it is corrupted
 (reflects the state during 'RSM' execution).

VMX doesn't have this problem because unlike VMCB, VMCS keeps both guest
and host state so when we switch back to VMCS02 L1's state is intact there.

To resolve the issue we need to save L1's state somewhere. We could've
created a third VMCB for SMM but that would require us to modify saved
state format. L1's architectural HSAVE area (pointed by MSR_VM_HSAVE_PA)
seems appropriate: L0 is free to save any (or none) of L1's state there.
Currently, KVM does 'none'.

Note, for nested state migration to succeed, both source and destination
hypervisors must have the fix. We, however, don't need to create a new
flag indicating the fact that HSAVE area is now populated as migration
during SMM triggered from L2 was always broken.

Fixes: 4995a368 ("KVM: SVM: Use a separate vmcb for the nested L2 guest")
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>