Re: [PATCH v5 05/13] KVM: selftests: Reuse GPR switching logic for nVMX

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly introduced VMX_SWITCH_GPRS_ASM macro uses a shared global variable `guest_regs` for swapping host and guest general-purpose registers, introducing a race condition when multiple vCPUs execute nested VMX instructions concurrently.
--

--- Patch [5]: [PATCH v5 05/13] KVM: selftests: Reuse GPR switching logic for nVMX ---
commit a0021d28e505a4c708c955c20d96663fad9fc879
Author: Yosry Ahmed <yosry@kernel.org>

KVM: selftests: Reuse GPR switching logic for nVMX

This commit reuses the SVM GPR switching logic for nVMX by defining
VMX_SWITCH_GPRS_ASM. It replaces the previous push/pop sequence with
macro calls that swap a broader set of registers using GUEST_SWITCH_GPR_ASM.

> diff --git a/tools/testing/selftests/kvm/include/x86/vmx.h b/tools/testing/selftests/kvm/include/x86/vmx.h
> --- a/tools/testing/selftests/kvm/include/x86/vmx.h
> +++ b/tools/testing/selftests/kvm/include/x86/vmx.h
> @@ -290,6 +290,23 @@ struct vmx_msr_entry {
>  	u64 value;
>  } __attribute__ ((aligned(16)));
>  
> +#define VMX_SWITCH_GPRS_ASM \
> +	GUEST_SWITCH_GPR_ASM(rax) \
> +	GUEST_SWITCH_GPR_ASM(rbx) \

[Severity: Medium]
Since GUEST_SWITCH_GPR_ASM() uses the global guest_regs structure, will this
cause a data race when multiple vCPUs execute nested VMX instructions
concurrently?

When vmlaunch or vmresume is executed concurrently by multiple threads (such
as in the memstress test), they might race to read and write to this shared
variable, potentially corrupting host callee-saved registers like rbx or r12.
Could this lead to host test code crashes when one vCPU restores another
vCPU's parked host registers?

> +	GUEST_SWITCH_GPR_ASM(rcx) \
> +	GUEST_SWITCH_GPR_ASM(rdx) \
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260728174232.2423257-1-yosry@kernel.org?part=5