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authorVipin Sharma <[email protected]>2022-09-21 23:24:51 -0700
committerSean Christopherson <[email protected]>2022-09-28 12:47:19 -0700
commitdfb45db43e9f6283a79230c8ea9cb589f14791b0 (patch)
tree17287a356e4a8301a239b7e1d341c23a03080b4b
parentbf3f11581893494a5fb01eb87b99627edc2a85ff (diff)
KVM: selftests: Load RAX with -EFAULT before Hyper-V hypercall
Load RAX with -EFAULT prior to making a Hyper-V hypercall so that tests can't get false negatives due to the compiler coincidentally loading the "right" value into RAX, i.e. to ensure that _KVM_ and not the compiler is correctly clearing RAX on a successful hypercall. Note, initializing *hv_status (in C code) to -EFAULT is not sufficient to avoid false negatives, as the compiler can still "clobber" RAX and thus load garbage into *hv_status if the hypercall faults (or if KVM doesn't set RAX). Suggested-by: Sean Christopherson <[email protected]> Signed-off-by: Vipin Sharma <[email protected]> Reviewed-by: Vitaly Kuznetsov <[email protected]> Link: https://lore.kernel.org/r/[email protected] [sean: move to separate patch, massage changelog] Signed-off-by: Sean Christopherson <[email protected]>
-rw-r--r--tools/testing/selftests/kvm/x86_64/hyperv_features.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_features.c b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
index ad01868548f9..4d55e038c2d7 100644
--- a/tools/testing/selftests/kvm/x86_64/hyperv_features.c
+++ b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
@@ -26,7 +26,8 @@ static inline uint8_t hypercall(u64 control, vm_vaddr_t input_address,
: "=a" (*hv_status),
"+c" (control), "+d" (input_address),
KVM_ASM_SAFE_OUTPUTS(vector)
- : [output_address] "r"(output_address)
+ : [output_address] "r"(output_address),
+ "a" (-EFAULT)
: "cc", "memory", "r8", KVM_ASM_SAFE_CLOBBERS);
return vector;
}