Messages in this thread | | | Date | Tue, 6 Feb 2024 20:03:24 -0800 | Subject | Re: [PATCH v12 08/20] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA | From | Sean Christopherson <> |
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+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@redhat.com
> + 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;
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