Re: [PATCH v2 19/28] KVM: Take memory protections into account for accesses with cached gfn->hva

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] kvm: loongarch build failure due to unrenamed ghc->generation field
--

commit d698f3639de00de4e2127e86617e1f29da8afef7
Author: Nicolas Saenz Julienne <nsaenz@amazon.com>

    KVM: Take memory protections into account for accesses with cached gfn->hva
    
    Account for memory attributes when accessing guest memory through
    kvm_get/put_guest().
    
    This requires tracking the memory attributes generation as part of
    gfn_to_hva_cache's data, invalidate the cached information if the
    generation changes, and failing to refresh the cache if restrictive
    memory attributes are found within the GPA range.

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2d85d7c9e0046..f10b14293e60e 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
[ ... ]
> @@ -3560,15 +3560,22 @@ static int __kvm_gfn_to_hva_cache_init(struct kvm *kvm,
>  	 * If the requested region crosses two memslots, we still
>  	 * verify that the entire region is valid here.
>  	 */
> -	for ( ; start_gfn <= end_gfn; start_gfn += nr_pages_avail) {
> -		ghc->memslot = __gfn_to_memslot(slots, start_gfn);
> -		ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn,
> -					   &nr_pages_avail);
> +	for (gfn_t gfn = start_gfn ; gfn <= end_gfn; gfn += nr_pages_avail) {
> +		ghc->memslot = __gfn_to_memslot(slots, gfn);
> +		ghc->hva = gfn_to_hva_many(ghc->memslot, gfn, &nr_pages_avail);
>  		if (kvm_is_error_hva(ghc->hva))
>  			return -EFAULT;
>  	}
>  
> +	/*
> +	 * RW memory attributes are incompatible with GHC. The RW protection
> +	 * check has to happen after storing the generation number.
> +	 */
>  	ghc->attrs_generation = kvm_mem_attributes_generation(kvm);

[Severity: Low]
Does this patchset break the build on LoongArch?

In arch/loongarch/kvm/vcpu.c, kvm_update_stolen_time() and
kvm_vcpu_set_pv_preempted() still reference the removed ghc->generation field
and fail to verify memory attribute generations:

arch/loongarch/kvm/vcpu.c:kvm_update_stolen_time() {
    ...
	if (slots->generation != ghc->generation || gpa != ghc->gpa) {
    ...
}

arch/loongarch/kvm/vcpu.c:kvm_vcpu_set_pv_preempted() {
    ...
	if (slots->generation != ghc->generation || gpa != ghc->gpa) {
    ...
}

With the transition to ghc->attrs_generation and ghc->slots_generation across
this patchset (specifically since the prior patch "KVM: Introduce a generation
number for memory attributes"), these manual generation checks will fail to
compile.

Could these be updated to use kvm_check_gen()?

> +	if (kvm_range_has_rw_memory_protections(kvm, start_gfn, end_gfn + 1)) {
> +		ghc->hva = KVM_HVA_ERR_BAD;
> +		return -EFAULT;
> +	}
>  
>  	/* Use the slow path for cross page reads and writes. */
>  	if (nr_pages_needed == 1)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260918081543.139871-1-pbonzini@redhat.com?part=19