* Willy Tarreau <[email protected]> wrote:
> When a syscall returns to userspace with pti_disable set, it means the
> current mm is configured to disable page table isolation (PTI). In this
> case, returns from kernel to user will not switch the CR3, leaving it
> to the kernel one which already maps both user and kernel pages. This
> avoids a TLB flush, and saves another one on next entry.
>
> Thanks to these changes, haproxy running under KVM went back from
> 12700 conn/s (without PCID) or 19700 (with PCID) to 23100 once loaded
> after calling prctl(), indicating that PTI has no measurable impact on
> this workload.
>
> Signed-off-by: Willy Tarreau <[email protected]>
> Cc: Andy Lutomirski <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Brian Gerst <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Linus Torvalds <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Josh Poimboeuf <[email protected]>
> Cc: "H. Peter Anvin" <[email protected]>
> Cc: Greg Kroah-Hartman <[email protected]>
> Cc: Kees Cook <[email protected]>
>
> v2:
> - use pti_disable instead of task flag
> ---
> arch/x86/entry/calling.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
> index 2c0d3b5..5361a10 100644
> --- a/arch/x86/entry/calling.h
> +++ b/arch/x86/entry/calling.h
> @@ -229,6 +229,11 @@
>
> .macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
> ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
> +
> + /* The "pti_disable" mm attribute is mirrored into this per-cpu var */
> + cmpb $0, PER_CPU_VAR(pti_disable)
> + jne .Lend_\@
Could you please do this small change for future iterations:
s/per-cpu
/per-CPU
... to make the spelling more consistent with the rest of the code base?
Thanks,
Ingo
