x86/xen: use capabilities instead of fake cpuid values for xsave

When running as pv domain xen_cpuid() is being used instead of
native_cpuid(). In xen_cpuid() the xsave feature availability is
indicated by special casing the related cpuid leaf.

Instead of delivering fake cpuid values set or clear the cpu
capability bits for xsave instead.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

1 files changed, 30 insertions, 23 deletions

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 38dec28a8e6d..a732bc2b9dfc 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -165,8 +165,6 @@ xen_running_on_version_or_later(unsigned int major, unsigned int minor)
         return false;
 }
 
-static __read_mostly unsigned int cpuid_leaf1_ecx_mask = ~0;
-
 static __read_mostly unsigned int cpuid_leaf5_ecx_val;
 static __read_mostly unsigned int cpuid_leaf5_edx_val;
 
@@ -174,16 +172,12 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
                       unsigned int *cx, unsigned int *dx)
 {
         unsigned maskebx = ~0;
-        unsigned maskecx = ~0;
+
         /*
          * Mask out inconvenient features, to try and disable as many
          * unsupported kernel subsystems as possible.
          */
         switch (*ax) {
-        case 1:
-                maskecx = cpuid_leaf1_ecx_mask;
-                break;
-
         case CPUID_MWAIT_LEAF:
                 /* Synthesize the values.. */
                 *ax = 0;
@@ -206,7 +200,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
                 : "0" (*ax), "2" (*cx));
 
         *bx &= maskebx;
-        *cx &= maskecx;
 }
 STACK_FRAME_NON_STANDARD(xen_cpuid); /* XEN_EMULATE_PREFIX */
 
@@ -281,22 +274,29 @@ static bool __init xen_check_mwait(void)
         return false;
 #endif
 }
-static void __init xen_init_cpuid_mask(void)
-{
-        unsigned int ax, bx, cx, dx;
-        unsigned int xsave_mask;
 
-        ax = 1;
-        cx = 0;
-        cpuid(1, &ax, &bx, &cx, &dx);
-
-        xsave_mask =
-                (1 << (X86_FEATURE_XSAVE % 32)) |
-                (1 << (X86_FEATURE_OSXSAVE % 32));
+static bool __init xen_check_xsave(void)
+{
+        unsigned int err, eax, edx;
 
-        /* Xen will set CR4.OSXSAVE if supported and not disabled by force */
-        if ((cx & xsave_mask) != xsave_mask)
-                cpuid_leaf1_ecx_mask &= ~xsave_mask; /* disable XSAVE & OSXSAVE */
+        /*
+         * Xen 4.0 and older accidentally leaked the host XSAVE flag into guest
+         * view, despite not being able to support guests using the
+         * functionality. Probe for the actual availability of XSAVE by seeing
+         * whether xgetbv executes successfully or raises #UD.
+         */
+        asm volatile("1: .byte 0x0f,0x01,0xd0\n\t" /* xgetbv */
+                     "xor %[err], %[err]\n"
+                     "2:\n\t"
+                     ".pushsection .fixup,\"ax\"\n\t"
+                     "3: movl $1,%[err]\n\t"
+                     "jmp 2b\n\t"
+                     ".popsection\n\t"
+                     _ASM_EXTABLE(1b, 3b)
+                     : [err] "=r" (err), "=a" (eax), "=d" (edx)
+                     : "c" (0));
+
+        return err == 0;
 }
 
 static void __init xen_init_capabilities(void)
@@ -316,6 +316,14 @@ static void __init xen_init_capabilities(void)
                 setup_force_cpu_cap(X86_FEATURE_MWAIT);
         else
                 setup_clear_cpu_cap(X86_FEATURE_MWAIT);
+
+        if (xen_check_xsave()) {
+                setup_force_cpu_cap(X86_FEATURE_XSAVE);
+                setup_force_cpu_cap(X86_FEATURE_OSXSAVE);
+        } else {
+                setup_clear_cpu_cap(X86_FEATURE_XSAVE);
+                setup_clear_cpu_cap(X86_FEATURE_OSXSAVE);
+        }
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)
@@ -1308,7 +1316,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
         xen_setup_gdt(0);
 
         xen_init_irq_ops();
-        xen_init_cpuid_mask();
         xen_init_capabilities();
 
 #ifdef CONFIG_X86_LOCAL_APIC