kvm: x86: Return LA57 feature based on hardware capability

commit 511da98d207d5c0675a10351b01e37cbe50a79e5 upstream.

Previously, 'commit 372fddf7 ("x86/mm: Introduce the 'no5lvl' kernel
parameter")' cleared X86_FEATURE_LA57 in boot_cpu_data, if Linux chooses
to not run in 5-level paging mode. Yet boot_cpu_data is queried by
do_cpuid_ent() as the host capability later when creating vcpus, and Qemu
will not be able to detect this feature and create VMs with LA57 feature.

As discussed earlier, VMs can still benefit from extended linear address
width, e.g. to enhance features like ASLR. So we would like to fix this,
by return the true hardware capability when Qemu queries.
Signed-off-by: NYu Zhang <yu.c.zhang@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/kvm/cpuid.c

@@ -337,6 +337,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 	unsigned f_mpx = kvm_mpx_supported() ? F(MPX) : 0;
 	unsigned f_xsaves = kvm_x86_ops->xsaves_supported() ? F(XSAVES) : 0;
 	unsigned f_umip = kvm_x86_ops->umip_emulated() ? F(UMIP) : 0;
+	unsigned f_la57 = 0;
 
 	/* cpuid 1.edx */
 	const u32 kvm_cpuid_1_edx_x86_features =
@@ -491,7 +492,10 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 			// TSC_ADJUST is emulated
 			entry->ebx |= F(TSC_ADJUST);
 			entry->ecx &= kvm_cpuid_7_0_ecx_x86_features;
+			f_la57 = entry->ecx & F(LA57);
 			cpuid_mask(&entry->ecx, CPUID_7_ECX);
+			/* Set LA57 based on hardware capability. */
+			entry->ecx |= f_la57;
 			entry->ecx |= f_umip;
 			/* PKU is not yet implemented for shadow paging. */
 			if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))