From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir@xen.org>
Subject: Re: [PATCH] x86/emulator: workaround for AMD erratum 573
Date: Thu, 15 Dec 2011 16:53:03 +0000
Message-ID: <CB0FD66F.36073%keir@xen.org>
References: <4EEA01350200007800068241@nat28.tlf.novell.com>
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To: Jan Beulich <JBeulich@suse.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

On 15/12/2011 13:16, "Jan Beulich" <JBeulich@suse.com> wrote:

> The only cases where we might end up emulating fsincos (as any other
> x87 operations without memory operands) are
> - when a HVM guest is in real mode (not applicable on AMD)
> - between two half page table updates in PAE mode (unlikely, and not
>   doing the emulation here does affect only performance, not
>   correctness)
> - when a guest maliciously (or erroneously) modifies an (MMIO or page
>   table update) instruction under emulation (unspecified behavior)
> 
> Hence, in order to avoid the erratum to cause harm to the entire host,
> don't emulate fsincos on the affected AMD CPU families.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Keir Fraser <keir@xen.org>

> --- a/tools/tests/x86_emulator/x86_emulate.c
> +++ b/tools/tests/x86_emulator/x86_emulate.c
> @@ -9,5 +9,7 @@ typedef bool bool_t;
>  
>  #define BUG() abort()
>  
> +#define cpu_has_amd_erratum(nr) 0
> +
>  #include "x86_emulate/x86_emulate.h"
>  #include "x86_emulate/x86_emulate.c"
> --- a/xen/arch/x86/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate.c
> @@ -10,8 +10,14 @@
>   */
>  
>  #include <asm/x86_emulate.h>
> +#include <asm/processor.h> /* current_cpu_info */
> +#include <asm/amd.h> /* cpu_has_amd_erratum() */
>  
>  /* Avoid namespace pollution. */
>  #undef cmpxchg
> +#undef cpuid
> +
> +#define cpu_has_amd_erratum(nr) \
> +        cpu_has_amd_erratum(&current_cpu_data, AMD_ERRATUM_##nr)
>  
>  #include "x86_emulate/x86_emulate.c"
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -2761,6 +2761,9 @@ x86_emulate(
>      case 0xd9: /* FPU 0xd9 */
>          switch ( modrm )
>          {
> +        case 0xfb: /* fsincos */
> +            fail_if(cpu_has_amd_erratum(573));
> +            /* fall through */
>          case 0xc0 ... 0xc7: /* fld %stN */
>          case 0xc8 ... 0xcf: /* fxch %stN */
>          case 0xd0: /* fnop */
> @@ -2786,7 +2789,6 @@ x86_emulate(
>          case 0xf8: /* fprem */
>          case 0xf9: /* fyl2xp1 */
>          case 0xfa: /* fsqrt */
> -        case 0xfb: /* fsincos */
>          case 0xfc: /* frndint */
>          case 0xfd: /* fscale */
>          case 0xfe: /* fsin */
> --- a/xen/include/asm-x86/amd.h
> +++ b/xen/include/asm-x86/amd.h
> @@ -134,6 +134,12 @@
>      AMD_OSVW_ERRATUM(3, AMD_MODEL_RANGE(0x10, 0x2, 0x1, 0xff, 0xf), \
>        AMD_MODEL_RANGE(0x12, 0x0, 0x0, 0x1, 0x0))
>  
> +#define AMD_ERRATUM_573       \
> +    AMD_LEGACY_ERRATUM(AMD_MODEL_RANGE(0x0f, 0x0, 0x0, 0xff, 0xf), \
> +                       AMD_MODEL_RANGE(0x10, 0x0, 0x0, 0xff, 0xf), \
> +                       AMD_MODEL_RANGE(0x11, 0x0, 0x0, 0xff, 0xf), \
> +                       AMD_MODEL_RANGE(0x12, 0x0, 0x0, 0xff, 0xf))
> +
>  struct cpuinfo_x86;
>  int cpu_has_amd_erratum(const struct cpuinfo_x86 *, int, ...);
>  
> 
> 
> 
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