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

BugLink: https://bugs.launchpad.net/bugs/1864775

[ Upstream commit e30a7d62 ]

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: ce88decf ("KVM: MMU: mmio page fault support")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/kvm/x86.c

@@ -6024,14 +6024,12 @@ static void kvm_set_mmio_spte_mask(void)
 	/* Set the present bit. */
 	mask |= 1ull;
 
-#ifdef CONFIG_X86_64
 	/*
 	 * If reserved bit is not supported, clear the present bit to disable
 	 * mmio page fault.
 	 */
 	if (maxphyaddr == 52)
 		mask &= ~1ull;
-#endif
 
 	kvm_mmu_set_mmio_spte_mask(mask);
 }