Re: [PATCH V3 0/7] x86/entry: Convert error_entry() to C code

[Lai Jiangshan]

On Mon, Jun 6, 2022 at 10:44 PM Lai Jiangshan <jiangshanlai@xxxxxxxxx> wrote:
>
> From: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
>
> Add some C equivalent functions of the ASM macros and implement the whole
> error_entry() as C code.
>
> The patches are picked and re-made from the huge patchset
> https://lore.kernel.org/lkml/20211126101209.8613-1-jiangshanlai@xxxxxxxxx/
> which converts a large chunk of ASM code to C code.
>
> The C version generally has better readability and easier to be
> updated/improved.
>
> This smaller patchset converts error_entry() only.
> The equivalent ASM macros are not removed because they are still used by
> the IST exceptions.
>
> No functional change intended and comments are also copied.
>
> The complier generates very similar code for the C code and the original
> ASM code except minor differences.
>
> The complier uses tail-call-optimization for calling sync_regs().  It
> uses "JMP sync_regs" while the ASM code uses "CALL+RET".
>
> The compiler generates "AND $0xe7,%ah" (3 bytes) for the code
> "cr3 = user_cr3 & ~PTI_USER_PGTABLE_AND_PCID_MASK" while the ASM code in
> SWITCH_TO_KERNEL_CR3() results "AND $0xffffffffffffe7ff,%rax" (6 bytes).
>
> The compiler generates lengthier code for "cr3 |= X86_CR3_PCID_NOFLUSH"
> because it uses "MOVABS+OR" (13 bytes)  rather than a single
> "BTS" (5 bytes).
>
> ALTERNATIVE and static_cpu_has() are also different which depends on
> what alternative instructions for ALTERNATIVE are.
>
> [V2]: https://lore.kernel.org/lkml/20220516131739.521817-1-jiangshanlai@xxxxxxxxx/
> [V1]: https://lore.kernel.org/lkml/20220511072747.3960-1-jiangshanlai@xxxxxxxxx/
>
> Changed from V2:
>         Fix conflict in arch/x86/include/asm/proto.h in patch7
>
> Changed from V1:
>         remove unneeded cleanup in patch2
>
> Changed from the old huge patchset:
>         squash some patches
>

Hello, ALL,

Ping

Thanks,
Lai