[Xen-devel] 回复: [PATCH] x86/spec_ctrl: Fix several bugs in SPEC_CTRL_ENTRY_FROM_INTR_IST

["zhenzhong.duan" <zhenzhong.duan@xxxxxxxxxx>]

2018年2月14日 19:10于 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>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.ostrovsky@xxxxxxxxxx>
> Reported-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> 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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