Re: [PATCH 5/6] KVM: PPC: Use CLASS(kvm_vcpu_map_local_readonly) for patching dcbz

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] The commit title claims to use `CLASS(kvm_vcpu_map_local_readonly)`, but the code uses the writable variant `CLASS(kvm_vcpu_map_local)`.
- [Low] The local variable `r` is declared but never used after the refactoring.
--

--- Patch [5]: [PATCH 5/6] KVM: PPC: Use CLASS(kvm_vcpu_map_local_readonly) for patching dcbz ---
commit 85b6110c0b5859c4a10a2a8a3cab84580d924a43
Author: Sean Christopherson <seanjc@google.com>

KVM: PPC: Use CLASS(kvm_vcpu_map_local_readonly) for patching dcbz

This commit converts the dcbz patching implementation in KVM PPC to use
the new scope-based CLASS(kvm_vcpu_map_local) infrastructure. It eliminates
the open-coded on-stack struct kvm_host_map to help harden the API against
memory leaks.

> KVM: PPC: Use CLASS(kvm_vcpu_map_local_readonly) for patching dcbz

[Severity: Medium]
The commit title mentions using CLASS(kvm_vcpu_map_local_readonly), but the
code below correctly uses the writable variant CLASS(kvm_vcpu_map_local)
since it needs to modify the memory. Should the title be updated to match
the implementation?

> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c

[ ... ]

>  static void kvmppc_patch_dcbz(struct kvm_vcpu *vcpu, struct kvmppc_pte *pte)
>  {
> -	struct kvm_host_map map;
>  	u64 hpage_offset;
>  	u32 *page;
>  	int i, r;

[Severity: Low]
Does this leave the variable r unused in kvmppc_patch_dcbz()?

It looks like the original call to kvm_vcpu_map() was replaced, and nothing
else assigns or reads r. This might cause a compiler warning for configurations
that check for unused variables.

> 
> -	r = kvm_vcpu_map(vcpu, pte->raddr >> PAGE_SHIFT, &map);
> -	if (r)
> +	CLASS(kvm_vcpu_map_local, m)(vcpu, pte->raddr >> PAGE_SHIFT);
> +	if (m.ret)
>  		return;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260724004757.131420-1-seanjc@google.com?part=5