[PATCH 3.16 61/99] KVM: x86/mmu: Apply max PA check for MMIO sptes to 32-bit KVM

[Ben Hutchings]

3.16.84-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

commit e30a7d623dccdb3f880fbcad980b0cb589a1da45 upstream.

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")
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5734,7 +5734,7 @@ 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) && maxphyaddr == 52)
+	if (maxphyaddr == 52)
 		mask &= ~1ull;
 
 	kvm_mmu_set_mmio_spte_mask(mask);