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KVM: Add support for read-only usage of gfn_to_page()

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Rework gfn_to_page() to support read-only accesses so that it can be used
by arm64 to get MTE tags out of guest memory.

Opportunistically rewrite the comment to be even more stern about using
gfn_to_page(), as there are very few scenarios where requiring a struct
page is actually the right thing to do (though there are such scenarios).
Add a FIXME to call out that KVM probably should be pinning pages, not
just getting pages.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-77-seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-10-10 11:24:18 -07:00 committed by Paolo Bonzini
parent ce6bf70346
commit f42e289a20
2 changed files with 14 additions and 8 deletions
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7
include/linux/kvm_host.h
View File

@ -1213,7 +1213,12 @@ void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
int kvm_prefetch_pages(struct kvm_memory_slot *slot, gfn_t gfn,
struct page **pages, int nr_pages);
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn, bool write);
static inline struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
{
return __gfn_to_page(kvm, gfn, true);
}
unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn);
unsigned long gfn_to_hva_prot(struct kvm *kvm, gfn_t gfn, bool *writable);
unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot, gfn_t gfn);

15
virt/kvm/kvm_main.c
View File

@ -3132,25 +3132,26 @@ int kvm_prefetch_pages(struct kvm_memory_slot *slot, gfn_t gfn,
EXPORT_SYMBOL_GPL(kvm_prefetch_pages);
/*
* Do not use this helper unless you are absolutely certain the gfn _must_ be
* backed by 'struct page'. A valid example is if the backing memslot is
* controlled by KVM. Note, if the returned page is valid, it's refcount has
* been elevated by gfn_to_pfn().
* Don't use this API unless you are absolutely, positively certain that KVM
* needs to get a struct page, e.g. to pin the page for firmware DMA.
*
* FIXME: Users of this API likely need to FOLL_PIN the page, not just elevate
* its refcount.
*/
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
struct page *__gfn_to_page(struct kvm *kvm, gfn_t gfn, bool write)
{
struct page *refcounted_page = NULL;
struct kvm_follow_pfn kfp = {
.slot = gfn_to_memslot(kvm, gfn),
.gfn = gfn,
.flags = FOLL_WRITE,
.flags = write ? FOLL_WRITE : 0,
.refcounted_page = &refcounted_page,
};
(void)kvm_follow_pfn(&kfp);
return refcounted_page;
}
EXPORT_SYMBOL_GPL(gfn_to_page);
EXPORT_SYMBOL_GPL(__gfn_to_page);
int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map,
bool writable)