[Xen-devel] [PATCH v3 09/11] x86/xen: use capabilities instead of fake cpuid values for xsave

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxx>
---
 arch/x86/xen/enlighten_pv.c | 46 +++++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 22 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 38dec28a8e6d..e6bf71d76e10 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 +274,24 @@ static bool __init xen_check_mwait(void)
        return false;
 #endif
 }
-static void __init xen_init_cpuid_mask(void)
+
+static bool __init xen_check_xsave(void)
 {
-       unsigned int ax, bx, cx, dx;
-       unsigned int xsave_mask;
+       unsigned int err, eax, edx;
 
-       ax = 1;
-       cx = 0;
-       cpuid(1, &ax, &bx, &cx, &dx);
+       /* Test OSXSAVE capability via xgetbv instruction. */
+       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));
 
-       xsave_mask =
-               (1 << (X86_FEATURE_XSAVE % 32)) |
-               (1 << (X86_FEATURE_OSXSAVE % 32));
-
-       /* 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 
*/
+       return err == 0;
 }
 
 static void __init xen_init_capabilities(void)
@@ -316,6 +311,14 @@ 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 +1311,6 @@ 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
-- 
2.12.0


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