KVM: SVM: Never reject emulation due to SMAP errata for !SEV guests

stable inclusion
from stable-v5.10.102
commit 9dcedbe943be8c93722c1ed68b59001b28b0d889
bugzilla: https://gitee.com/openeuler/kernel/issues/I567K6

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9dcedbe943be8c93722c1ed68b59001b28b0d889

--------------------------------

commit 55467fcd upstream.

Always signal that emulation is possible for !SEV guests regardless of
whether or not the CPU provided a valid instruction byte stream.  KVM can
read all guest state (memory and registers) for !SEV guests, i.e. can
fetch the code stream from memory even if the CPU failed to do so because
of the SMAP errata.

Fixes: 05d5a486 ("KVM: SVM: Workaround errata#1096 (insn_len maybe zero on SMAP violation)")
Cc: stable@vger.kernel.org
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Reviewed-by: NLiam Merwick <liam.merwick@oracle.com>
Message-Id: <20220120010719.711476-2-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
[jwang: adjust context for kernel 5.10.101]
Signed-off-by: NJack Wang <jinpu.wang@ionos.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/x86/kvm/svm/svm.c

@@ -4103,6 +4103,10 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int i
 	bool smep, smap, is_user;
 	unsigned long cr4;
 
+	/* Emulation is always possible when KVM has access to all guest state. */
+	if (!sev_guest(vcpu->kvm))
+		return true;
+
 	/*
 	 * Detect and workaround Errata 1096 Fam_17h_00_0Fh.
 	 *
@@ -4151,9 +4155,6 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int i
 	smap = cr4 & X86_CR4_SMAP;
 	is_user = svm_get_cpl(vcpu) == 3;
 	if (smap && (!smep || is_user)) {
-		if (!sev_guest(vcpu->kvm))
-			return true;
-
 		pr_err_ratelimited("KVM: SEV Guest triggered AMD Erratum 1096\n");
 
 		/*