[PATCH 19/19] KVM: MMU: Fix potential race setting upper shadow ptes on nonpae hosts

[Avi Kivity]

The direct mapped shadow code (used for real mode and two dimensional paging)
sets upper-level ptes using direct assignment rather than calling
set_shadow_pte().  A nonpae host will split this into two writes, which opens
up a race if another vcpu accesses the same memory area.

Fix by calling set_shadow_pte() instead of assigning directly.

Noticed by Izik Eidus.

Signed-off-by: Avi Kivity <avi@xxxxxxxxxxxx>
---
 arch/x86/kvm/mmu.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7f57da6..b0e4ddc 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1189,9 +1189,10 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 				return -ENOMEM;
 			}
 
-			table[index] = __pa(new_table->spt)
-				| PT_PRESENT_MASK | PT_WRITABLE_MASK
-				| shadow_user_mask | shadow_x_mask;
+			set_shadow_pte(&table[index],
+				       __pa(new_table->spt)
+				       | PT_PRESENT_MASK | PT_WRITABLE_MASK
+				       | shadow_user_mask | shadow_x_mask);
 		}
 		table_addr = table[index] & PT64_BASE_ADDR_MASK;
 	}
-- 
1.5.6.1

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