KVM: VMX: Set IGMT bit in EPT entry

There is a potential issue that, when guest using pagetable without vmexit when
EPT enabled, guest would use PAT/PCD/PWT bits to index PAT msr for it's memory,
which would be inconsistent with host side and would cause host MCE due to
inconsistent cache attribute.

The patch set IGMT bit in EPT entry to ignore guest PAT and use WB as default
memory type to protect host (notice that all memory mapped by KVM should be WB).
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -3564,7 +3564,8 @@ static int __init vmx_init(void)
 		bypass_guest_pf = 0;
 		kvm_mmu_set_base_ptes(VMX_EPT_READABLE_MASK |
 			VMX_EPT_WRITABLE_MASK |
-			VMX_EPT_DEFAULT_MT << VMX_EPT_MT_EPTE_SHIFT);
+			VMX_EPT_DEFAULT_MT << VMX_EPT_MT_EPTE_SHIFT |
+			VMX_EPT_IGMT_BIT);
 		kvm_mmu_set_mask_ptes(0ull, 0ull, 0ull, 0ull,
 				VMX_EPT_EXECUTABLE_MASK);
 		kvm_enable_tdp();

arch/x86/kvm/vmx.h

@@ -352,6 +352,7 @@ enum vmcs_field {
 #define VMX_EPT_READABLE_MASK			0x1ull
 #define VMX_EPT_WRITABLE_MASK			0x2ull
 #define VMX_EPT_EXECUTABLE_MASK			0x4ull
+#define VMX_EPT_IGMT_BIT    			(1ull << 6)
 
 #define VMX_EPT_IDENTITY_PAGETABLE_ADDR		0xfffbc000ul