[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3 09/11] x86/xen: use capabilities instead of fake cpuid values for xsave
On 04/21/2017 10:45 AM, Andrew Cooper wrote: > On 21/04/17 15:38, Juergen Gross wrote: >> On 21/04/17 16:24, Boris Ostrovsky wrote: >>>> +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)); >>> Have you tested this on processors where we actually trap on xgetbv? >>> >>> I have an AMD box without XSAVE support and this is a fatal error. I >>> suspect it's too early to use exception fixup framework here. >> Uuh, too bad. >> >> Then I fear we must use the other solution Andrew didn't like. :-( >> Andrew, would you be okay with that? > Hmm fine. The status quo is probably best then to unblock this series. > > As an independent question, why are exceptions set up so late? They > really should be the very first thing done It's exception fixup that is not set up yet --- we are executing here before "main" kernel's entry point. This is somewhat similar to what arch/x86/kernel/head_64.S:early_idt_handler_common() does --- it has special handling for early fixup --- early_fixup_exception(). I wonder though --- can this feature masking be deferred until a bit later? -boris _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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