Re: [PATCH v3 2/2] KVM: LoongArch: selftests: Add FPU test case

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] FPU selftest fails to verify that `vcpu_fpu_set` actually modifies the vCPU FPU state.
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commit 2bf4caa3158a9fa987285bf7aea2092fe7c8a3f7
Author: Bibo Mao <maobibo@loongson.cn>

KVM: LoongArch: selftests: Add FPU test case

This commit adds an FPU test case to verify FPU register get and set APIs
for LoongArch. It supports testing 64, 128, and 256-bit FPU widths.

> diff --git a/tools/testing/selftests/kvm/loongarch/fpu_test.c b/tools/testing/selftests/kvm/loongarch/fpu_test.c
> new file mode 100644
> index 0000000000000..fe58ed4f93c0b
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/loongarch/fpu_test.c

[ ... ]

> +int main(void)
> +{

[ ... ]

> +	fpu.fpr[0].val64[0] += random();
> +	vcpu_fpu_set(vcpu, &fpu);
> +	run_vcpu(vcpu);
> +	vcpu_fpu_get(vcpu, &fpu);
> +	sync_global_from_guest(vm, *fp);
> +	TEST_ASSERT(!memcmp(fpu.fpr, fp, 8), "Wanted 0x%llx from f0, got 0x%llx",
> +			fp->val64[0], fpu.fpr[0].val64[0]);

[Severity: Medium]
Does this sequence actually verify the set operation? 

The test adds random() to the fpu structure and calls vcpu_fpu_set(). However,
it then updates both the fpu structure via vcpu_fpu_get() and the fp structure
via sync_global_from_guest() before comparing them against each other.

If vcpu_fpu_set() silently fails or does nothing, won't both structures just
read back the previous, unmodified state and cause the memcmp() to pass anyway?
It looks like this pattern repeats for the 128-bit and 256-bit checks below as
well.

> +
> +	fpu.fpr[0].val64[0] += random();
> +	fpu.fpr[0].val64[1] += random();
> +	vcpu_fpu_set(vcpu, &fpu);
> +	run_vcpu(vcpu);
> +	vcpu_fpu_get(vcpu, &fpu);
> +	sync_global_from_guest(vm, *fp);
> +	TEST_ASSERT(!memcmp(fpu.fpr, fp, 16), "Wanted 0x%llx %llx from vr0, got 0x%llx %llx",
> +			fp->val64[0], fp->val64[1],
> +			fpu.fpr[0].val64[0], fpu.fpr[0].val64[1]);

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616022615.2141072-1-maobibo@loongson.cn?part=2