[PATCH] KVM: x86/mmu: Apply max PA check for MMIO sptes to 32-bit KVM

[PATCH] KVM: x86/mmu: Apply max PA check for MMIO sptes to 32-bit KVM

[Sean Christopherson]

Remove the bogus 64-bit only condition from the check that disables MMIO
spte optimization when the system supports the max PA, i.e. doesn't have
any reserved PA bits.  32-bit KVM always uses PAE paging for the shadow
MMU, and per Intel's SDM:

  PAE paging translates 32-bit linear addresses to 52-bit physical
  addresses.

The kernel's restrictions on max physical addresses are limits on how
much memory the kernel can reasonably use, not what physical addresses
are supported by hardware.

Fixes: ce88decffd17 ("KVM: MMU: mmio page fault support")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7269130ea5e2..d9c07343d979 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6191,7 +6191,7 @@ static void kvm_set_mmio_spte_mask(void)
 	 * If reserved bit is not supported, clear the present bit to disable
 	 * mmio page fault.
 	 */
-	if (IS_ENABLED(CONFIG_X86_64) && shadow_phys_bits == 52)
+	if (shadow_phys_bits == 52)
 		mask &= ~1ull;
 
 	kvm_mmu_set_mmio_spte_mask(mask, mask, ACC_WRITE_MASK | ACC_USER_MASK);
-- 
2.24.1

Re: [PATCH] KVM: x86/mmu: Apply max PA check for MMIO sptes to 32-bit KVM

[Paolo Bonzini]

On 08/01/20 01:12, Sean Christopherson wrote:
> Remove the bogus 64-bit only condition from the check that disables MMIO
> spte optimization when the system supports the max PA, i.e. doesn't have
> any reserved PA bits.  32-bit KVM always uses PAE paging for the shadow
> MMU, and per Intel's SDM:
> 
>   PAE paging translates 32-bit linear addresses to 52-bit physical
>   addresses.
> 
> The kernel's restrictions on max physical addresses are limits on how
> much memory the kernel can reasonably use, not what physical addresses
> are supported by hardware.
> 
> Fixes: ce88decffd17 ("KVM: MMU: mmio page fault support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 7269130ea5e2..d9c07343d979 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -6191,7 +6191,7 @@ static void kvm_set_mmio_spte_mask(void)
>  	 * If reserved bit is not supported, clear the present bit to disable
>  	 * mmio page fault.
>  	 */
> -	if (IS_ENABLED(CONFIG_X86_64) && shadow_phys_bits == 52)
> +	if (shadow_phys_bits == 52)
>  		mask &= ~1ull;
>  
>  	kvm_mmu_set_mmio_spte_mask(mask, mask, ACC_WRITE_MASK | ACC_USER_MASK);
> 

Queued, thanks.

Paolo