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KVM: SVM: Override default MMIO mask if memory encryption is enabled 

The KVM MMIO support uses bit 51 as the reserved bit to cause nested page
faults when a guest performs MMIO. The AMD memory encryption support uses
a CPUID function to define the encryption bit position. Given this, it is
possible that these bits can conflict.

Use svm_hardware_setup() to override the MMIO mask if memory encryption
support is enabled. Various checks are performed to ensure that the mask
is properly defined and rsvd_bits() is used to generate the new mask (as
was done prior to the change that necessitated this patch).

Fixes: 28a1f3ac1d ("kvm: x86: Set highest physical address bits in non-present/reserved SPTEs")
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Tom Lendacky 2020-01-09 17:42:16 -06:00 committed by Paolo Bonzini
parent d8010a779a
commit 52918ed5fc
1 changed files with 43 additions and 0 deletions
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43
arch/x86/kvm/svm.c
View File

@ -1307,6 +1307,47 @@ static void shrink_ple_window(struct kvm_vcpu *vcpu)
}
}
/*
* The default MMIO mask is a single bit (excluding the present bit),
* which could conflict with the memory encryption bit. Check for
* memory encryption support and override the default MMIO mask if
* memory encryption is enabled.
*/
static __init void svm_adjust_mmio_mask(void)
{
unsigned int enc_bit, mask_bit;
u64 msr, mask;
/* If there is no memory encryption support, use existing mask */
if (cpuid_eax(0x80000000) < 0x8000001f)
return;
/* If memory encryption is not enabled, use existing mask */
rdmsrl(MSR_K8_SYSCFG, msr);
if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
return;
enc_bit = cpuid_ebx(0x8000001f) & 0x3f;
mask_bit = boot_cpu_data.x86_phys_bits;
/* Increment the mask bit if it is the same as the encryption bit */
if (enc_bit == mask_bit)
mask_bit++;
/*
* If the mask bit location is below 52, then some bits above the
* physical addressing limit will always be reserved, so use the
* rsvd_bits() function to generate the mask. This mask, along with
* the present bit, will be used to generate a page fault with
* PFER.RSV = 1.
*
* If the mask bit location is 52 (or above), then clear the mask.
*/
mask = (mask_bit < 52) ? rsvd_bits(mask_bit, 51) | PT_PRESENT_MASK : 0;
kvm_mmu_set_mmio_spte_mask(mask, mask, PT_WRITABLE_MASK | PT_USER_MASK);
}
static __init int svm_hardware_setup(void)
{
int cpu;
@ -1361,6 +1402,8 @@ static __init int svm_hardware_setup(void)
}
}
svm_adjust_mmio_mask();
for_each_possible_cpu(cpu) {
r = svm_cpu_init(cpu);
if (r)