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KVM: guest_memfd: Add hook for invalidating memory

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In some cases, like with SEV-SNP, guest memory needs to be updated in a
platform-specific manner before it can be safely freed back to the host.
Wire up arch-defined hooks to the .free_folio kvm_gmem_aops callback to
allow for special handling of this sort when freeing memory in response
to FALLOC_FL_PUNCH_HOLE operations and when releasing the inode, and go
ahead and define an arch-specific hook for x86 since it will be needed
for handling memory used for SEV-SNP guests.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Message-Id: <20231230172351.574091-6-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Michael Roth 2023-12-30 11:23:21 -06:00 committed by Paolo Bonzini
parent 1f6c06b177
commit a90764f0e4
6 changed files with 31 additions and 0 deletions
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1
arch/x86/include/asm/kvm-x86-ops.h
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@ -140,6 +140,7 @@ KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
KVM_X86_OP_OPTIONAL(get_untagged_addr)
KVM_X86_OP_OPTIONAL(alloc_apic_backing_page)
KVM_X86_OP_OPTIONAL_RET0(gmem_prepare)
KVM_X86_OP_OPTIONAL(gmem_invalidate)
#undef KVM_X86_OP
#undef KVM_X86_OP_OPTIONAL

1
arch/x86/include/asm/kvm_host.h
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@ -1813,6 +1813,7 @@ struct kvm_x86_ops {
gva_t (*get_untagged_addr)(struct kvm_vcpu *vcpu, gva_t gva, unsigned int flags);
void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu);
int (*gmem_prepare)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order);
void (*gmem_invalidate)(kvm_pfn_t start, kvm_pfn_t end);
};
struct kvm_x86_nested_ops {

7
arch/x86/kvm/x86.c
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@ -13605,6 +13605,13 @@ int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_ord
}
#endif
#ifdef CONFIG_HAVE_KVM_GMEM_INVALIDATE
void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end)
{
static_call_cond(kvm_x86_gmem_invalidate)(start, end);
}
#endif
int kvm_spec_ctrl_test_value(u64 value)
{
/*

4
include/linux/kvm_host.h
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@ -2475,4 +2475,8 @@ typedef int (*kvm_gmem_populate_cb)(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
long kvm_gmem_populate(struct kvm *kvm, gfn_t gfn, void __user *src, long npages,
kvm_gmem_populate_cb post_populate, void *opaque);
#ifdef CONFIG_HAVE_KVM_GMEM_INVALIDATE
void kvm_arch_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
#endif
#endif

4
virt/kvm/Kconfig
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@ -113,3 +113,7 @@ config KVM_GENERIC_PRIVATE_MEM
config HAVE_KVM_GMEM_PREPARE
bool
depends on KVM_PRIVATE_MEM
config HAVE_KVM_GMEM_INVALIDATE
bool
depends on KVM_PRIVATE_MEM

14
virt/kvm/guest_memfd.c
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@ -343,10 +343,24 @@ static int kvm_gmem_error_folio(struct address_space *mapping, struct folio *fol
return MF_DELAYED;
}
#ifdef CONFIG_HAVE_KVM_GMEM_INVALIDATE
static void kvm_gmem_free_folio(struct folio *folio)
{
struct page *page = folio_page(folio, 0);
kvm_pfn_t pfn = page_to_pfn(page);
int order = folio_order(folio);
kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order));
}
#endif
static const struct address_space_operations kvm_gmem_aops = {
.dirty_folio = noop_dirty_folio,
.migrate_folio = kvm_gmem_migrate_folio,
.error_remove_folio = kvm_gmem_error_folio,
#ifdef CONFIG_HAVE_KVM_GMEM_INVALIDATE
.free_folio = kvm_gmem_free_folio,
#endif
};
static int kvm_gmem_getattr(struct mnt_idmap *idmap, const struct path *path,