Re: [PATCH v10 02/25] x86/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT

Laurent Dufour [off-list ref] writes:

On 08/05/2018 13:04, Punit Agrawal wrote:

quoted

Hi Laurent,

Laurent Dufour [off-list ref] writes:

quoted

Set ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT which turns on the
Speculative Page Fault handler when building for 64bit.

Cc: Thomas Gleixner <redacted>
Signed-off-by: Laurent Dufour <redacted>
---
 arch/x86/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index d8983df5a2bc..ebdeb48e4a4a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -30,6 +30,7 @@ config X86_64
 	select MODULES_USE_ELF_RELA
 	select X86_DEV_DMA_OPS
 	select ARCH_HAS_SYSCALL_WRAPPER
+	select ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT

I'd suggest merging this patch with the one making changes to the
architectural fault handler towards the end of the series.

The Kconfig change is closely tied to the architectural support for SPF
and makes sense to be in a single patch.

If there's a good reason to keep them as separate patches, please move
the architecture Kconfig changes after the patch adding fault handler
changes.

It's better to enable the feature once the core infrastructure is merged
rather than at the beginning of the series to avoid potential bad
fallout from incomplete functionality during bisection.

Indeed bisection was the reason why Andrew asked me to push the configuration
enablement on top of the series (https://lkml.org/lkml/2017/10/10/1229).

The config options have gone through another round of splitting (between
core and architecture) since that comment. I agree that it still makes
sense to define the core config - CONFIG_SPECULATIVE_PAGE_FAULT early
on.

Just to clarify, my suggestion was to only move the architecture configs
further down.

I also think it would be better to have the architecture enablement in on patch
but that would mean that the code will not be build when bisecting without the
latest patch adding the per architecture code.

I don't see that as a problem. But if I'm in the minority, I am OK with
leaving things as they are as well.

Thanks,
Punit