Commit 3bb2531e authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: guest_memfd: Add hook for initializing memory 

guest_memfd pages are generally expected to be in some arch-defined
initial state prior to using them for guest memory. For SEV-SNP this
initial state is 'private', or 'guest-owned', and requires additional
operations to move these pages into a 'private' state by updating the
corresponding entries the RMP table.

Allow for an arch-defined hook to handle updates of this sort, and go
ahead and implement one for x86 so KVM implementations like AMD SVM can
register a kvm_x86_ops callback to handle these updates for SEV-SNP
guests.

The preparation callback is always called when allocating/grabbing
folios via gmem, and it is up to the architecture to keep track of
whether or not the pages are already in the expected state (e.g. the RMP
table in the case of SEV-SNP).

In some cases, it is necessary to defer the preparation of the pages to
handle things like in-place encryption of initial guest memory payloads
before marking these pages as 'private'/'guest-owned'.  Add an argument
(always true for now) to kvm_gmem_get_folio() that allows for the
preparation callback to be bypassed.  To detect possible issues in
the way userspace initializes memory, it is only possible to add an
unprepared page if it is not already included in the filemap.

Link: https://lore.kernel.org/lkml/ZLqVdvsF11Ddo7Dq@google.com/


Co-developed-by: default avatarMichael Roth <michael.roth@amd.com>
Signed-off-by: default avatarMichael Roth <michael.roth@amd.com>
Message-Id: <20231230172351.574091-5-michael.roth@amd.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent fa30b0dc

arch/x86/include/asm/kvm-x86-ops.h

+1 −0
Original line number Diff line number Diff line
@@ -139,6 +139,7 @@ KVM_X86_OP(vcpu_deliver_sipi_vector) 
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)



#undef KVM_X86_OP

#undef KVM_X86_OP_OPTIONAL

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -1812,6 +1812,7 @@ 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);

};



struct kvm_x86_nested_ops {

arch/x86/kvm/x86.c

+6 −0
Original line number Diff line number Diff line
@@ -13598,6 +13598,12 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) 
}

EXPORT_SYMBOL_GPL(kvm_arch_no_poll);



#ifdef CONFIG_HAVE_KVM_GMEM_PREPARE

int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order)

{

	return static_call(kvm_x86_gmem_prepare)(kvm, pfn, gfn, max_order);

}

#endif



int kvm_spec_ctrl_test_value(u64 value)

{

include/linux/kvm_host.h

+5 −0
Original line number Diff line number Diff line
@@ -2443,4 +2443,9 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm, 
}

#endif /* CONFIG_KVM_PRIVATE_MEM */



#ifdef CONFIG_HAVE_KVM_GMEM_PREPARE

int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order);

bool kvm_arch_gmem_prepare_needed(struct kvm *kvm);

#endif



#endif

virt/kvm/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -109,3 +109,7 @@ config KVM_GENERIC_PRIVATE_MEM 
       select KVM_GENERIC_MEMORY_ATTRIBUTES

       select KVM_PRIVATE_MEM

       bool



config HAVE_KVM_GMEM_PREPARE

       bool

       depends on KVM_PRIVATE_MEM