KVM: nVMX: Clear reserved bits of #DB exit qualification

[ Upstream commit cfb634f ] According to volume 3 of the SDM, bits 63:15 and 12:4 of the exit qualification field for debug exceptions are reserved (cleared to 0). However, the SDM is incorrect about bit 16 (corresponding to DR6.RTM). This bit should be set if a debug exception (#DB) or a breakpoint exception (#BP) occurred inside an RTM region while advanced debugging of RTM transactional regions was enabled. Note that this is the opposite of DR6.RTM, which "indicates (when clear) that a debug exception (#DB) or breakpoint exception (#BP) occurred inside an RTM region while advanced debugging of RTM transactional regions was enabled." There is still an issue with stale DR6 bits potentially being misreported for the current debug exception. DR6 should not have been modified before vectoring the #DB exception, and the "new DR6 bits" should be available somewhere, but it was and they aren't. Fixes: b96fb43 ("KVM: nVMX: fixes to nested virt interrupt injection") Signed-off-by: Jim Mattson <[email protected]> Reviewed-by: Sean Christopherson <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
maraz · Nov 13, 2018 · 7d6c6f8 · 7d6c6f8
1 parent be5658a
commit 7d6c6f8
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Showing 2 changed files with 6 additions and 2 deletions.
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
@@ -174,6 +174,7 @@ enum {
 
 #define DR6_BD		(1 << 13)
 #define DR6_BS		(1 << 14)
+#define DR6_BT		(1 << 15)
 #define DR6_RTM		(1 << 16)
 #define DR6_FIXED_1	0xfffe0ff0
 #define DR6_INIT	0xffff0ff0

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
@@ -2733,10 +2733,13 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned long *exit
 		}
 	} else {
 		if (vmcs12->exception_bitmap & (1u << nr)) {
-			if (nr == DB_VECTOR)
+			if (nr == DB_VECTOR) {
 				*exit_qual = vcpu->arch.dr6;
-			else
+				*exit_qual &= ~(DR6_FIXED_1 | DR6_BT);
+				*exit_qual ^= DR6_RTM;
+			} else {
 				*exit_qual = 0;
+			}
 			return 1;
 		}
 	}