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KVM: x86: Use guest MAXPHYADDR from CPUID.0x8000_0008 iff TDP is enabled

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Ignore the guest MAXPHYADDR reported by CPUID.0x8000_0008 if TDP, i.e.
NPT, is disabled, and instead use the host's MAXPHYADDR.  Per AMD'S APM:

  Maximum guest physical address size in bits. This number applies only
  to guests using nested paging. When this field is zero, refer to the
  PhysAddrSize field for the maximum guest physical address size.

Fixes: 24c82e576b ("KVM: Sanitize cpuid")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210623230552.4027702-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-06-23 16:05:46 -07:00 committed by Paolo Bonzini
parent f0414b078d
commit 4bf48e3c0a
1 changed files with 7 additions and 1 deletions
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8
arch/x86/kvm/cpuid.c
View file

@ -940,8 +940,14 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
unsigned virt_as = max((entry->eax >> 8) & 0xff, 48U);
unsigned phys_as = entry->eax & 0xff;
if (!g_phys_as)
/*
* Use bare metal's MAXPHADDR if the CPU doesn't report guest
* MAXPHYADDR separately, or if TDP (NPT) is disabled, as the
* guest version "applies only to guests using nested paging".
*/
if (!g_phys_as || !tdp_enabled)
g_phys_as = phys_as;
entry->eax = g_phys_as | (virt_as << 8);
entry->edx = 0;
cpuid_entry_override(entry, CPUID_8000_0008_EBX);