Re: [PATCH v4 1/2] RISC-V: KVM: add tracepoint for guest page faults

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly added `kvm_page_fault` tracepoint misses MMIO accesses and instruction access faults because it is placed after the early-return paths in `gstage_page_fault()`.
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commit 9a1dfc5717473462915b50774722a5444137d7bd
Author: Wang Yechao <wang.yechao255@zte.com.cn>

RISC-V: KVM: add tracepoint for guest page faults

This commit adds the kvm_page_fault event tracepoint to count the number
of KVM guest page faults on RISC-V.

> diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
> index 88e0c369b3544..8f44e27563f85 100644
> --- a/arch/riscv/kvm/vcpu_exit.c
> +++ b/arch/riscv/kvm/vcpu_exit.c
> @@ -64,6 +64,8 @@ static int gstage_page_fault(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  		};
>  	}
>  
> +	trace_kvm_page_fault(vcpu, fault_addr, trap->scause);

[Severity: Medium]
Does this placement miss MMIO accesses and instruction access faults?

If a guest page fault resolves to an MMIO region or an unmapped instruction
fetch, the early return paths in gstage_page_fault() will handle the fault
and return before reaching this tracepoint.

For example, when an error HVA is encountered:

	if (kvm_is_error_hva(hva) || ...) {
		switch (trap->scause) {
		case EXC_LOAD_GUEST_PAGE_FAULT:
			return kvm_riscv_vcpu_mmio_load(...);
		...
		};
	}

	trace_kvm_page_fault(vcpu, fault_addr, trap->scause);

Could this cause incorrect statistics for users monitoring KVM guest page
faults, since it skips all page faults that fall into those early returns?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260913070352.3626956-1-wang.yechao255@zte.com.cn?part=1