KVM: SEV: sync FPU and AVX state at LAUNCH_UPDATE_VMSA time

SEV-ES allows passing custom contents for x87, SSE and AVX state into the VMSA.
Allow userspace to do that with the usual KVM_SET_XSAVE API and only mark
FPU contents as confidential after it has been copied and encrypted into
the VMSA.

Since the XSAVE state for AVX is the first, it does not need the
compacted-state handling of get_xsave_addr().  However, there are other
parts of XSAVE state in the VMSA that currently are not handled, and
the validation logic of get_xsave_addr() is pointless to duplicate
in KVM, so move get_xsave_addr() to public FPU API; it is really just
a facility to operate on XSAVE state and does not expose any internal
details of arch/x86/kernel/fpu.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240404121327.3107131-12-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 50 insertions, 8 deletions

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 1512bacd74a9..3517d6736c93 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -23,6 +23,7 @@
 #include <asm/pkru.h>
 #include <asm/trapnr.h>
 #include <asm/fpu/xcr.h>
+#include <asm/fpu/xstate.h>
 #include <asm/debugreg.h>
 
 #include "mmu.h"
@@ -584,6 +585,10 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 	struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
 	struct sev_es_save_area *save = svm->sev_es.vmsa;
+	struct xregs_state *xsave;
+	const u8 *s;
+	u8 *d;
+	int i;
 
 	/* Check some debug related fields before encrypting the VMSA */
 	if (svm->vcpu.guest_debug || (svm->vmcb->save.dr7 & ~DR7_FIXED_1))
@@ -626,6 +631,44 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
 
 	save->sev_features = sev->vmsa_features;
 
+	/*
+	 * Skip FPU and AVX setup with KVM_SEV_ES_INIT to avoid
+	 * breaking older measurements.
+	 */
+	if (vcpu->kvm->arch.vm_type != KVM_X86_DEFAULT_VM) {
+		xsave = &vcpu->arch.guest_fpu.fpstate->regs.xsave;
+		save->x87_dp = xsave->i387.rdp;
+		save->mxcsr = xsave->i387.mxcsr;
+		save->x87_ftw = xsave->i387.twd;
+		save->x87_fsw = xsave->i387.swd;
+		save->x87_fcw = xsave->i387.cwd;
+		save->x87_fop = xsave->i387.fop;
+		save->x87_ds = 0;
+		save->x87_cs = 0;
+		save->x87_rip = xsave->i387.rip;
+
+		for (i = 0; i < 8; i++) {
+			/*
+			 * The format of the x87 save area is undocumented and
+			 * definitely not what you would expect.  It consists of
+			 * an 8*8 bytes area with bytes 0-7, and an 8*2 bytes
+			 * area with bytes 8-9 of each register.
+			 */
+			d = save->fpreg_x87 + i * 8;
+			s = ((u8 *)xsave->i387.st_space) + i * 16;
+			memcpy(d, s, 8);
+			save->fpreg_x87[64 + i * 2] = s[8];
+			save->fpreg_x87[64 + i * 2 + 1] = s[9];
+		}
+		memcpy(save->fpreg_xmm, xsave->i387.xmm_space, 256);
+
+		s = get_xsave_addr(xsave, XFEATURE_YMM);
+		if (s)
+			memcpy(save->fpreg_ymm, s, 256);
+		else
+			memset(save->fpreg_ymm, 0, 256);
+	}
+
 	pr_debug("Virtual Machine Save Area (VMSA):\n");
 	print_hex_dump_debug("", DUMP_PREFIX_NONE, 16, 1, save, sizeof(*save), false);
 
@@ -664,6 +707,13 @@ static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu,
 	if (ret)
 	  return ret;
 
+	/*
+	 * SEV-ES guests maintain an encrypted version of their FPU
+	 * state which is restored and saved on VMRUN and VMEXIT.
+	 * Mark vcpu->arch.guest_fpu->fpstate as scratch so it won't
+	 * do xsave/xrstor on it.
+	 */
+	fpstate_set_confidential(&vcpu->arch.guest_fpu);
 	vcpu->arch.guest_state_protected = true;
 	return 0;
 }
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b0038ece55cb..0f3b59da0d4a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1433,14 +1433,6 @@ static int svm_vcpu_create(struct kvm_vcpu *vcpu)
 		vmsa_page = snp_safe_alloc_page(vcpu);
 		if (!vmsa_page)
 			goto error_free_vmcb_page;
-
-		/*
-		 * SEV-ES guests maintain an encrypted version of their FPU
-		 * state which is restored and saved on VMRUN and VMEXIT.
-		 * Mark vcpu->arch.guest_fpu->fpstate as scratch so it won't
-		 * do xsave/xrstor on it.
-		 */
-		fpstate_set_confidential(&vcpu->arch.guest_fpu);
 	}
 
 	err = avic_init_vcpu(svm);