linux-kernel - [RFC PATCH v2 10/13] KVM: x86: Let moving encryption context be configurable

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Message-ID: <7c51d4ae251323ce8c224aa362a4be616b4cfeba.1747368093.git.afranji@google.com>
Date: Fri, 16 May 2025 19:19:30 +0000
From: Ryan Afranji <afranji@...gle.com>
To: afranji@...gle.com, ackerleytng@...gle.com, pbonzini@...hat.com, 
	seanjc@...gle.com, tglx@...utronix.de, x86@...nel.org, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	tabba@...gle.com
Cc: mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, 
	shuah@...nel.org, andrew.jones@...ux.dev, ricarkol@...gle.com, 
	chao.p.peng@...ux.intel.com, jarkko@...nel.org, yu.c.zhang@...ux.intel.com, 
	vannapurve@...gle.com, erdemaktas@...gle.com, mail@...iej.szmigiero.name, 
	vbabka@...e.cz, david@...hat.com, qperret@...gle.com, michael.roth@....com, 
	wei.w.wang@...el.com, liam.merwick@...cle.com, isaku.yamahata@...il.com, 
	kirill.shutemov@...ux.intel.com, sagis@...gle.com, jthoughton@...gle.com
Subject: [RFC PATCH v2 10/13] KVM: x86: Let moving encryption context be configurable

From: Ackerley Tng <ackerleytng@...gle.com>

SEV-capable VMs may also use the KVM_X86_SW_PROTECTED_VM type, but
they will still need architecture-specific handling to move encryption
context. Hence, we let moving of encryption context be configurable
and store that configuration in a flag.

Co-developed-by: Vishal Annapurve <vannapurve@...gle.com>
Signed-off-by: Vishal Annapurve <vannapurve@...gle.com>
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Signed-off-by: Ryan Afranji <afranji@...gle.com>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/svm/sev.c          | 2 ++
 arch/x86/kvm/x86.c              | 9 ++++++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 179618300270..db37ce814611 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1576,6 +1576,7 @@ struct kvm_arch {
 #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
 	struct kvm_mmu_memory_cache split_desc_cache;
 
+	bool use_vm_enc_ctxt_op;
 	gfn_t gfn_direct_bits;
 
 	/*
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 689521d9e26f..95083556d321 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -442,6 +442,8 @@ static int __sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp,
 	if (ret)
 		goto e_no_asid;
 
+	kvm->arch.use_vm_enc_ctxt_op = true;
+
 	init_args.probe = false;
 	ret = sev_platform_init(&init_args);
 	if (ret)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 637540309456..3a7e05c47aa8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6624,7 +6624,14 @@ static int kvm_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
 	if (r)
 		goto out_mark_migration_done;
 
-	r = kvm_x86_call(vm_move_enc_context_from)(kvm, source_kvm);
+	/*
+	 * Different types of VMs will allow userspace to define if moving
+	 * encryption context should be required.
+	 */
+	if (kvm->arch.use_vm_enc_ctxt_op &&
+	    kvm_x86_ops.vm_move_enc_context_from) {
+		r = kvm_x86_call(vm_move_enc_context_from)(kvm, source_kvm);
+	}
 
 	kvm_unlock_two_vms(kvm, source_kvm);
 out_mark_migration_done:
-- 
2.49.0.1101.gccaa498523-goog