On Mon, Dec 19, 2022 at 12:00:08PM +0000, Tong Tiangen wrote: > At present, Recover from poison consumption from copy-on-write has been > supported[1], arm64 should also support this mechanism. > > Add new helper copy_mc_page() which provide a page copy implementation with > machine check safe. At present, only used in cow. In the future, we can > expand more scenes. As long as the consequences of page copy failure are > not fatal(eg: only affect user process), we can use this helper. > > The copy_mc_page() in copy_page_mc.S is largely borrows from copy_page() > in copy_page.S and the main difference is copy_mc_page() add extable entry > to every load/store insn to support machine check safe. largely to keep the > patch simple. If needed those optimizations can be folded in. > > Add new extable type EX_TYPE_COPY_MC_PAGE which used in copy_mc_page(). > > [1]https://lore.kernel.org/lkml/20221031201029.102123-1-tony.luck@xxxxxxxxx/ > > Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx> This series needs rebasing onto a newer kernel. Some random comments below. > diff --git a/arch/arm64/lib/copy_mc_page.S b/arch/arm64/lib/copy_mc_page.S > new file mode 100644 > index 000000000000..03d657a182f6 > --- /dev/null > +++ b/arch/arm64/lib/copy_mc_page.S > @@ -0,0 +1,82 @@ [...] > +SYM_FUNC_START(__pi_copy_mc_page) > +alternative_if ARM64_HAS_NO_HW_PREFETCH > + // Prefetch three cache lines ahead. > + prfm pldl1strm, [x1, #128] > + prfm pldl1strm, [x1, #256] > + prfm pldl1strm, [x1, #384] > +alternative_else_nop_endif > + > +CPY_MC(9998f, ldp x2, x3, [x1]) > +CPY_MC(9998f, ldp x4, x5, [x1, #16]) > +CPY_MC(9998f, ldp x6, x7, [x1, #32]) > +CPY_MC(9998f, ldp x8, x9, [x1, #48]) > +CPY_MC(9998f, ldp x10, x11, [x1, #64]) > +CPY_MC(9998f, ldp x12, x13, [x1, #80]) > +CPY_MC(9998f, ldp x14, x15, [x1, #96]) > +CPY_MC(9998f, ldp x16, x17, [x1, #112]) [...] [...] > +9998: ret What I don't understand, is there any error returned here or the bytes not copied? I can see its return value is never used in this series. Also, do we need to distinguish between fault on the source or the destination? > diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S > index 5018ac03b6bf..bf4dd861c41c 100644 > --- a/arch/arm64/lib/mte.S > +++ b/arch/arm64/lib/mte.S > @@ -80,6 +80,25 @@ SYM_FUNC_START(mte_copy_page_tags) > ret > SYM_FUNC_END(mte_copy_page_tags) > > +/* > + * Copy the tags from the source page to the destination one wiht machine check safe > + * x0 - address of the destination page > + * x1 - address of the source page > + */ > +SYM_FUNC_START(mte_copy_mc_page_tags) > + mov x2, x0 > + mov x3, x1 > + multitag_transfer_size x5, x6 > +1: > +CPY_MC(2f, ldgm x4, [x3]) > + stgm x4, [x2] > + add x2, x2, x5 > + add x3, x3, x5 > + tst x2, #(PAGE_SIZE - 1) > + b.ne 1b > +2: ret > +SYM_FUNC_END(mte_copy_mc_page_tags) While the data copy above handles errors on both source and destination, here you skip the destination. Any reason? > diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c > index 8dd5a8fe64b4..005ee2a3cb4e 100644 > --- a/arch/arm64/mm/copypage.c > +++ b/arch/arm64/mm/copypage.c [...] > +#ifdef CONFIG_ARCH_HAS_COPY_MC > +void copy_mc_highpage(struct page *to, struct page *from) > +{ > + void *kto = page_address(to); > + void *kfrom = page_address(from); > + > + copy_mc_page(kto, kfrom); > + do_mte(to, from, kto, kfrom, true); > +} > +EXPORT_SYMBOL(copy_mc_highpage); > + > +int copy_mc_user_highpage(struct page *to, struct page *from, > + unsigned long vaddr, struct vm_area_struct *vma) > +{ > + copy_mc_highpage(to, from); > + flush_dcache_page(to); > + return 0; > +} This one always returns 0. Does it actually catch any memory failures? > +EXPORT_SYMBOL_GPL(copy_mc_user_highpage); > +#endif > diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c > index 28ec35e3d210..0fdab18f2f07 100644 > --- a/arch/arm64/mm/extable.c > +++ b/arch/arm64/mm/extable.c > @@ -16,6 +16,13 @@ get_ex_fixup(const struct exception_table_entry *ex) > return ((unsigned long)&ex->fixup + ex->fixup); > } > > +static bool ex_handler_fixup(const struct exception_table_entry *ex, > + struct pt_regs *regs) > +{ > + regs->pc = get_ex_fixup(ex); > + return true; > +} Should we prepare some error here like -EFAULT? That's done in ex_handler_uaccess_err_zero(). -- Catalin
