2018年2月14日 19:10于 Andrew Cooper <andrew.coop...@citrix.com>写道:
>
> DO_OVERWRITE_RSB clobbers %rax, meaning in practice that that the 
> bti_ist_info 
> field gets zeroed.  Older versions of this code had the DO_OVERWRITE_RSB 
> register selectable, so reintroduce this ability and use it to cause the 
> INTR_IST path to use %rdx instead. 
>
> The use of %dl for the %cs.rpl check means that when an IST interrupt hits 
> Xen, we try to load 1 into the high 32 bits of MSR_SPEC_CTRL, suffering a #GP 
> fault instead. 
>
> Also, drop an unused label which was a copy/paste mistake. 
>
> Reported-by: Boris Ostrovsky <boris.ostrov...@oracle.com> 
> Reported-by: Zhenzhong Duan <zhenzhong.d...@oracle.com> 
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> 
> --- 
> CC: Jan Beulich <jbeul...@suse.com> 
> CC: Zhenzhong Duan <zhenzhong.d...@oracle.com> 
> CC: Boris Ostrovsky <boris.ostrov...@oracle.com> 
> CC: Wei Liu <wei.l...@citrix.com> 
> CC: Roger Pau Monné <roger....@citrix.com> 
> --- 
> xen/include/asm-x86/spec_ctrl_asm.h | 12 ++++++------ 
> 1 file changed, 6 insertions(+), 6 deletions(-) 
>
> diff --git a/xen/include/asm-x86/spec_ctrl_asm.h 
> b/xen/include/asm-x86/spec_ctrl_asm.h 
> index 814f53d..1f78599 100644 
> --- a/xen/include/asm-x86/spec_ctrl_asm.h 
> +++ b/xen/include/asm-x86/spec_ctrl_asm.h 
> @@ -79,10 +79,10 @@ 
>   *  - SPEC_CTRL_EXIT_TO_GUEST 
>   */ 
>
> -.macro DO_OVERWRITE_RSB 
> +.macro DO_OVERWRITE_RSB tmp=%rax 
> /* 
>   * Requires nothing 
> - * Clobbers %rax, %rcx 
> + * Clobbers \tmp (%rax by default), %rcx 
>   * 
>   * Requires 256 bytes of stack space, but %rsp has no net change. Based on 
>   * Google's performance numbers, the loop is unrolled to 16 iterations and 
> two 
> @@ -97,7 +97,7 @@ 
>   * optimised with mov-elimination in modern cores. 
>   */ 
>      mov $16, %ecx                   /* 16 iterations, two calls per loop */ 
> -    mov %rsp, %rax                  /* Store the current %rsp */ 
> +    mov %rsp, \tmp                  /* Store the current %rsp */ 
>
> .L\@_fill_rsb_loop: 
>
> @@ -114,7 +114,7 @@ 
>
>      sub $1, %ecx 
>      jnz .L\@_fill_rsb_loop 
> -    mov %rax, %rsp                  /* Restore old %rsp */ 
> +    mov \tmp, %rsp                  /* Restore old %rsp */ 
> .endm 
>
> .macro DO_SPEC_CTRL_ENTRY_FROM_VMEXIT ibrs_val:req 
> @@ -274,7 +274,7 @@ 
>      testb $BTI_IST_RSB, %al 
>      jz .L\@_skip_rsb 
>
> -    DO_OVERWRITE_RSB 
> +    DO_OVERWRITE_RSB tmp=%rdx /* Clobbers %ecx/%rdx */ 
>
> .L\@_skip_rsb: 
>
> @@ -286,13 +286,13 @@ 
>      setz %dl 
>      and %dl, STACK_CPUINFO_FIELD(use_shadow_spec_ctrl)(%r14) 
Is it safe to remove the 'xor %edx, %edx' above? setz set whole byte 1 or 0.
---
thanks
zduan

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