From 6807cf65f5ba6f2902ab64355d71506b9c14a9dd Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Wed, 12 Apr 2017 15:12:09 +0200 Subject: [PATCH] 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 Reviewed-by: Andrew Cooper Signed-off-by: Juergen Gross --- arch/x86/xen/enlighten_pv.c | 53 +++++++++++++++++++++---------------- 1 file 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 -- 2.20.1