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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Feb 14, 2018 at 11:10:55AM +0000, Andrew Cooper wrote:
> 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>

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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