target/i386: Populate x86_ext_save_areas offsets using cpuid where possible

Rather than relying on the X86XSaveArea structure definition,
determine the offset of XSAVE state areas using CPUID leaf 0xd where
possible (KVM and HVF).

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20210705104632.2902400-8-david.edmondson@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 37 insertions, 0 deletions

diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
index 00369c2000..bbe817764d 100644
--- a/target/i386/kvm/kvm-cpu.c
+++ b/target/i386/kvm/kvm-cpu.c
@@ -122,6 +122,34 @@ static void kvm_cpu_max_instance_init(X86CPU *cpu)
         kvm_arch_get_supported_cpuid(s, 0xC0000000, 0, R_EAX);
 }
 
+static void kvm_cpu_xsave_init(void)
+{
+    static bool first = true;
+    KVMState *s = kvm_state;
+    int i;
+
+    if (!first) {
+        return;
+    }
+    first = false;
+
+    /* x87 and SSE states are in the legacy region of the XSAVE area. */
+    x86_ext_save_areas[XSTATE_FP_BIT].offset = 0;
+    x86_ext_save_areas[XSTATE_SSE_BIT].offset = 0;
+
+    for (i = XSTATE_SSE_BIT + 1; i < XSAVE_STATE_AREA_COUNT; i++) {
+        ExtSaveArea *esa = &x86_ext_save_areas[i];
+
+        if (esa->size) {
+            int sz = kvm_arch_get_supported_cpuid(s, 0xd, i, R_EAX);
+            if (sz != 0) {
+                assert(esa->size == sz);
+                esa->offset = kvm_arch_get_supported_cpuid(s, 0xd, i, R_EBX);
+            }
+        }
+    }
+}
+
 static void kvm_cpu_instance_init(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);
@@ -141,6 +169,8 @@ static void kvm_cpu_instance_init(CPUState *cs)
     if (cpu->max_features) {
         kvm_cpu_max_instance_init(cpu);
     }
+
+    kvm_cpu_xsave_init();
 }
 
 static void kvm_cpu_accel_class_init(ObjectClass *oc, void *data)
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 41b0764ab7..a85035492f 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1891,6 +1891,13 @@ int kvm_arch_init_vcpu(CPUState *cs)
         env->xsave_buf_len = sizeof(struct kvm_xsave);
         env->xsave_buf = qemu_memalign(4096, env->xsave_buf_len);
         memset(env->xsave_buf, 0, env->xsave_buf_len);
+
+        /*
+         * The allocated storage must be large enough for all of the
+         * possible XSAVE state components.
+         */
+        assert(kvm_arch_get_supported_cpuid(kvm_state, 0xd, 0, R_ECX)
+               <= env->xsave_buf_len);
     }
 
     max_nested_state_len = kvm_max_nested_state_length();