Re: [PATCH v2 0/6] Enable LKGS instruction

[H. Peter Anvin]

On 10/10/22 12:01, Xin Li wrote:
> LKGS instruction is introduced with Intel FRED (flexible return and event
> delivery) specification https://cdrdv2.intel.com/v1/dl/getContent/678938.
>
> LKGS is independent of FRED, so we enable it as a standalone CPU feature.
>
> LKGS behaves like the MOV to GS instruction except that it loads the base
> address into the IA32_KERNEL_GS_BASE MSR instead of the GS segment’s
> descriptor cache, which is exactly what Linux kernel does to load user level
> GS base.  Thus, with LKGS, there is no need to SWAPGS away from the kernel
> GS base.
>
> Changes since V1:
> * place fixup code into code section "__ex_table" instead of the obsoleted
>    "fixup" section.

Correction: __ex_table is NOT a code section (scared me there for a 
second...). With the new fixup handling code EX_TYPE_ZERO_REG takes care 
of all the work, and there simply is no need for any fixup code at all 
(the exception fixup is fully data-driven.)

So I would say "use EX_TYPE_ZERO_REG instead of fixup code in the 
obsolete .fixup code section."

	-hpa