Re: [PATCH v3] hvf: guard xgetbv call.

From: Cameron Esfahani <dirty@apple.com>
To: Hill Ma <maahiuzeon@gmail.com>
Cc: r.bolshakov@yadro.com, richard.henderson@linaro.org,
	qemu-devel@nongnu.org
Subject: Re: [PATCH v3] hvf: guard xgetbv call.
Date: Tue, 19 Jan 2021 19:04:14 -0800	[thread overview]
Message-ID: <F4AF1D4E-5DC8-4F83-BB4B-6059A19C59B1@apple.com> (raw)
In-Reply-To: <X/6OJ7qk0W6bHkHQ@Hills-Mac-Pro.local>

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Reviewed-by: Cameron Esfahani <dirty@apple.com <mailto:dirty@apple.com>>

Cameron Esfahani
dirty@apple.com

> On Jan 12, 2021, at 10:07 PM, Hill Ma <maahiuzeon@gmail.com> wrote:
> 
> This prevents illegal instruction on cpus do not support xgetbv.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1758819
> Signed-off-by: Hill Ma <maahiuzeon@gmail.com>
> ---
> v3: addressed feedback.
> v2: xgetbv() modified based on feedback.
> 
> target/i386/hvf/x86_cpuid.c | 34 ++++++++++++++++++++++------------
> 1 file changed, 22 insertions(+), 12 deletions(-)
> 
> diff --git a/target/i386/hvf/x86_cpuid.c b/target/i386/hvf/x86_cpuid.c
> index a6842912f5..32b0d131df 100644
> --- a/target/i386/hvf/x86_cpuid.c
> +++ b/target/i386/hvf/x86_cpuid.c
> @@ -27,15 +27,22 @@
> #include "vmx.h"
> #include "sysemu/hvf.h"
> 
> -static uint64_t xgetbv(uint32_t xcr)
> +static bool xgetbv(uint32_t cpuid_ecx, uint32_t idx, uint64_t *xcr)
> {
> -    uint32_t eax, edx;
> +    uint32_t xcrl, xcrh;
> 
> -    __asm__ volatile ("xgetbv"
> -                      : "=a" (eax), "=d" (edx)
> -                      : "c" (xcr));
> +    if (cpuid_ecx & CPUID_EXT_OSXSAVE) {
> +        /*
> +         * The xgetbv instruction is not available to older versions of
> +         * the assembler, so we encode the instruction manually.
> +         */
> +        asm(".byte 0x0f, 0x01, 0xd0" : "=a" (xcrl), "=d" (xcrh) : "c" (idx));
> 
> -    return (((uint64_t)edx) << 32) | eax;
> +        *xcr = (((uint64_t)xcrh) << 32) | xcrl;
> +        return true;
> +    }
> +
> +    return false;
> }
> 
> uint32_t hvf_get_supported_cpuid(uint32_t func, uint32_t idx,
> @@ -100,12 +107,15 @@ uint32_t hvf_get_supported_cpuid(uint32_t func, uint32_t idx,
>         break;
>     case 0xD:
>         if (idx == 0) {
> -            uint64_t host_xcr0 = xgetbv(0);
> -            uint64_t supp_xcr0 = host_xcr0 & (XSTATE_FP_MASK | XSTATE_SSE_MASK |
> -                                  XSTATE_YMM_MASK | XSTATE_BNDREGS_MASK |
> -                                  XSTATE_BNDCSR_MASK | XSTATE_OPMASK_MASK |
> -                                  XSTATE_ZMM_Hi256_MASK | XSTATE_Hi16_ZMM_MASK);
> -            eax &= supp_xcr0;
> +            uint64_t host_xcr0;
> +            if (xgetbv(ecx, 0, &host_xcr0)) {
> +                uint64_t supp_xcr0 = host_xcr0 & (XSTATE_FP_MASK |
> +                                  XSTATE_SSE_MASK | XSTATE_YMM_MASK |
> +                                  XSTATE_BNDREGS_MASK | XSTATE_BNDCSR_MASK |
> +                                  XSTATE_OPMASK_MASK | XSTATE_ZMM_Hi256_MASK |
> +                                  XSTATE_Hi16_ZMM_MASK);
> +                eax &= supp_xcr0;
> +            }
>         } else if (idx == 1) {
>             hv_vmx_read_capability(HV_VMX_CAP_PROCBASED2, &cap);
>             eax &= CPUID_XSAVE_XSAVEOPT | CPUID_XSAVE_XGETBV1;
> -- 
> 2.20.1 (Apple Git-117)
> 


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