+s390 folks (question on kvm_is_error_gpa() for ya)
On Mon, Jan 15, 2024, Paul Durrant wrote:
> @@ -1398,7 +1414,9 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
> static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
> {
> lockdep_assert_held(&gpc->lock);
> - mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> +
> + if (gpc->gpa != KVM_XEN_INVALID_GPA)
KVM_XEN_INVALID_GPA absolutely doesn't belong in common code. Not to mention
that it will break when Paolo (rightly) moves it to an x86 header.
https://lore.kernel.org/all/20240131233056.10845-3-pbonzini@xxxxxxxxxx
> + mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> }
>
> void kvm_sigset_activate(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
> index 97eec8ee3449..ae822bff812f 100644
> --- a/virt/kvm/pfncache.c
> +++ b/virt/kvm/pfncache.c
> @@ -48,7 +48,10 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
> if (!gpc->active)
> return false;
>
> - if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
> + if (gpc->gpa != KVM_XEN_INVALID_GPA && gpc->generation != slots->generation)
This needs a comment. I know what it's doing, but it wasn't obvious at first
glance, and it definitely won't be intuitive for readers that aren't intimately
familiar with memslots.
> + return false;
> +
> + if (kvm_is_error_hva(gpc->uhva))
> return false;
>
> if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
> @@ -209,11 +212,13 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
> return -EFAULT;
> }
>
> -static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
> +static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
> unsigned long len)
> {
> struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
> - unsigned long page_offset = offset_in_page(gpa);
> + unsigned long page_offset = (gpa != KVM_XEN_INVALID_GPA) ?
> + offset_in_page(gpa) :
> + offset_in_page(uhva);
This formatting is funky. I also think it would be worth adding a helper to pair
with kvm_is_error_hva().
But! kvm_is_error_gpa() already exists, and it very, very sneakily does a memslot
lookup and checks for a valid HVA.
s390 people, any objection to renaming kvm_is_error_gpa() to something like
kvm_gpa_has_memslot() or kvm_gpa_is_in_memslot()? s390 is the only code that
uses the existing helper.
That would both to free up the name to pair with kvm_is_error_hva(), and would
make it obvious what the helper does; I was quite surprised that "error" means
"is covered by a valid memslot".
Back to this code, then we can have a slightly cleaner:
unsigned long page_offset = kvm_is_error_gpa(gpa) ? offset_in_page(gpa) :
offset_in_page(uhva);
And I think it's worth asserting that exactly _one_ of GPA or HVA is valid, e.g.
to ensure KVM doesn't end up with botched offsets, and to make it a bit more
clear what's going on.
if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva))
return -EINVAL;
