Re: [PATCH v13 4/5] arm64: support copy_mc_[user]_highpage()

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Feb 14, 2025 at 10:49:01AM +0800, Tong Tiangen wrote:
> 在 2025/2/13 1:11, Catalin Marinas 写道:
> > On Mon, Dec 09, 2024 at 10:42:56AM +0800, Tong Tiangen wrote:
> > > Currently, many scenarios that can tolerate memory errors when copying page
> > > have been supported in the kernel[1~5], all of which are implemented by
> > > copy_mc_[user]_highpage(). arm64 should also support this mechanism.
> > > 
> > > Due to mte, arm64 needs to have its own copy_mc_[user]_highpage()
> > > architecture implementation, macros __HAVE_ARCH_COPY_MC_HIGHPAGE and
> > > __HAVE_ARCH_COPY_MC_USER_HIGHPAGE have been added to control it.
> > > 
> > > Add new helper copy_mc_page() which provide a page copy implementation with
> > > hardware memory error safe. The code logic of copy_mc_page() is the same as
> > > copy_page(), the main difference is that the ldp insn of copy_mc_page()
> > > contains the fixup type EX_TYPE_KACCESS_ERR_ZERO_MEM_ERR, therefore, the
> > > main logic is extracted to copy_page_template.S. In addition, the fixup of
> > > MOPS insn is not considered at present.
> > 
> > Could we not add the exception table entry permanently but ignore the
> > exception table entry if it's not on the do_sea() path? That would save
> > some code duplication.
> 
> I'm sorry, I didn't catch your point, that the do_sea() and non do_sea()
> paths use different exception tables?

No, they would have the same exception table, only that we'd interpret
it differently depending on whether it's a SEA error or not. Or rather
ignore the exception table altogether for non-SEA errors.

> My understanding is that the
> exception table entry problem is fine. After all, the search is
> performed only after a fault trigger. Code duplication can be solved by
> extracting repeated logic to a public file.

If the new exception table entries are only taken into account for SEA
errors, why do we need a duplicate copy_mc_page() function generated?
Isn't the copy_page() and copy_mc_page() code identical (except for the
additional labels to jump to for the exception)?

-- 
Catalin