Commit 8eb01900 authored by Michael Roth's avatar Michael Roth Committed by Paolo Bonzini
Browse files

KVM: SEV: Implement gmem hook for invalidating private pages 



Implement a platform hook to do the work of restoring the direct map
entries of gmem-managed pages and transitioning the corresponding RMP
table entries back to the default shared/hypervisor-owned state.

Signed-off-by: default avatarMichael Roth <michael.roth@amd.com>
Message-ID: <20240501085210.2213060-15-michael.roth@amd.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4f2e7aa1

arch/x86/kvm/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -138,6 +138,7 @@ config KVM_AMD_SEV 
	select ARCH_HAS_CC_PLATFORM

	select KVM_GENERIC_PRIVATE_MEM

	select HAVE_KVM_GMEM_PREPARE

	select HAVE_KVM_GMEM_INVALIDATE

	help

	  Provides support for launching Encrypted VMs (SEV) and Encrypted VMs

	  with Encrypted State (SEV-ES) on AMD processors.

arch/x86/kvm/svm/sev.c

+64 −0
Original line number Diff line number Diff line
@@ -4663,3 +4663,67 @@ int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order) 


	return 0;

}



void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end)

{

	kvm_pfn_t pfn;



	pr_debug("%s: PFN start 0x%llx PFN end 0x%llx\n", __func__, start, end);



	for (pfn = start; pfn < end;) {

		bool use_2m_update = false;

		int rc, rmp_level;

		bool assigned;



		rc = snp_lookup_rmpentry(pfn, &assigned, &rmp_level);

		if (WARN_ONCE(rc, "SEV: Failed to retrieve RMP entry for PFN 0x%llx error %d\n",

			      pfn, rc))

			goto next_pfn;



		if (!assigned)

			goto next_pfn;



		use_2m_update = IS_ALIGNED(pfn, PTRS_PER_PMD) &&

				end >= (pfn + PTRS_PER_PMD) &&

				rmp_level > PG_LEVEL_4K;



		/*

		 * If an unaligned PFN corresponds to a 2M region assigned as a

		 * large page in the RMP table, PSMASH the region into individual

		 * 4K RMP entries before attempting to convert a 4K sub-page.

		 */

		if (!use_2m_update && rmp_level > PG_LEVEL_4K) {

			/*

			 * This shouldn't fail, but if it does, report it, but

			 * still try to update RMP entry to shared and pray this

			 * was a spurious error that can be addressed later.

			 */

			rc = snp_rmptable_psmash(pfn);

			WARN_ONCE(rc, "SEV: Failed to PSMASH RMP entry for PFN 0x%llx error %d\n",

				  pfn, rc);

		}



		rc = rmp_make_shared(pfn, use_2m_update ? PG_LEVEL_2M : PG_LEVEL_4K);

		if (WARN_ONCE(rc, "SEV: Failed to update RMP entry for PFN 0x%llx error %d\n",

			      pfn, rc))

			goto next_pfn;



		/*

		 * SEV-ES avoids host/guest cache coherency issues through

		 * WBINVD hooks issued via MMU notifiers during run-time, and

		 * KVM's VM destroy path at shutdown. Those MMU notifier events

		 * don't cover gmem since there is no requirement to map pages

		 * to a HVA in order to use them for a running guest. While the

		 * shutdown path would still likely cover things for SNP guests,

		 * userspace may also free gmem pages during run-time via

		 * hole-punching operations on the guest_memfd, so flush the

		 * cache entries for these pages before free'ing them back to

		 * the host.

		 */

		clflush_cache_range(__va(pfn_to_hpa(pfn)),

				    use_2m_update ? PMD_SIZE : PAGE_SIZE);

next_pfn:

		pfn += use_2m_update ? PTRS_PER_PMD : 1;

		cond_resched();

	}

}

arch/x86/kvm/svm/svm.c

+1 −0
Original line number Diff line number Diff line
@@ -5083,6 +5083,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { 
	.alloc_apic_backing_page = svm_alloc_apic_backing_page,



	.gmem_prepare = sev_gmem_prepare,

	.gmem_invalidate = sev_gmem_invalidate,

};



/*

arch/x86/kvm/svm/svm.h

+2 −0
Original line number Diff line number Diff line
@@ -737,6 +737,7 @@ void sev_handle_rmp_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code); 
void sev_vcpu_unblocking(struct kvm_vcpu *vcpu);

void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu);

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

void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);

#else

static inline struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu) {

	return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
@@ -757,6 +758,7 @@ static inline int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, in 
{

	return 0;

}

static inline void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end) {}



#endif