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Re: [PATCH] x86/entry: Use 32bit XOR in handle_ist_exception
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Nov 2023 09:56:55 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Nov 2023 08:57:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.11.2023 20:57, Andrew Cooper wrote:
> This is a micro-optimsiation for Silvermont microarchitectures, which don't
> recognise the 64bit form as a zeroing idiom.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
For my education, ...
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -1027,7 +1027,7 @@ handle_ist_exception:
> * Interrupted guest context. Clear the restore value for xen_cr3
> * and copy the context to stack bottom.
> */
> - xor %r15, %r15
> + xor %r15d, %r15d
> xor %ebx, %ebx
> GET_CPUINFO_FIELD(guest_cpu_user_regs,di)
> movq %rsp,%rsi
>
> base-commit: fa2da5bce90b3777aa7a323e1cf201c97b56d278
... while I understand this, what ...
> prerequisite-patch-id: a9e4e1e34d08e876d1fcb3299c6d563086768722
> prerequisite-patch-id: 703590f2c99382f6509c94bb5955f47ab2d7c57d
... are these about? They look like they would be naming prereq changes
which aren't committed yet, but (a) base-commit names the tip of the
staging branch and (b) the hashes would be meaningless without a repo
reference if they pointed at something that wasn't committed yet.
Jan
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