Commit f42e289a authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

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



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: default avatarAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Tested-by: default avatarDmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-77-seanjc@google.com>
parent ce6bf703

include/linux/kvm_host.h

+6 −1
Original line number Diff line number Diff line
@@ -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);

virt/kvm/kvm_main.c

+8 −7
Original line number Diff line number Diff line
@@ -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)