[Xen-devel] [PATCH v2 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 | 28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 38dec28a8e6d..dad1db61e40b 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 +274,19 @@ 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 cx, xsave_mask;
 
-       ax = 1;
-       cx = 0;
-       cpuid(1, &ax, &bx, &cx, &dx);
+       cx = cpuid_ecx(1);
 
        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 (cx & xsave_mask) == xsave_mask;
 }
 
 static void __init xen_init_capabilities(void)
@@ -316,6 +306,11 @@ 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_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 +1303,6 @@ 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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