On 17/05/2023 03:21, Peter Collingbourne wrote: > As a result of the previous two patches, there are no circumstances > in which a swapped-in page is installed in a page table without first > having arch_swap_restore() called on it. Therefore, we no longer need > the logic in set_pte_at() that restores the tags, so remove it. > > Because we can now rely on the page being locked, we no longer need to > handle the case where a page is having its tags restored by multiple tasks > concurrently, so we can slightly simplify the logic in mte_restore_tags(). > > Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx> > Link: https://linux-review.googlesource.com/id/I8ad54476f3b2d0144ccd8ce0c1d7a2963e5ff6f3 This is much neater, thanks for figuring out a better way of implementing it. The set_pte_at() thing always felt like a hack, but it was always there for the non-swap case and I obviously never figured out a better solution. Reviewed-by: Steven Price <steven.price@xxxxxxx> > --- > v3: > - Rebased onto arm64/for-next/fixes, which already has a fix > for the issue previously tagged, therefore removed Fixes: > tag > > arch/arm64/include/asm/mte.h | 4 ++-- > arch/arm64/include/asm/pgtable.h | 14 ++---------- > arch/arm64/kernel/mte.c | 37 ++++++-------------------------- > arch/arm64/mm/mteswap.c | 7 +++--- > 4 files changed, 14 insertions(+), 48 deletions(-) > > diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h > index c028afb1cd0b..4cedbaa16f41 100644 > --- a/arch/arm64/include/asm/mte.h > +++ b/arch/arm64/include/asm/mte.h > @@ -90,7 +90,7 @@ static inline bool try_page_mte_tagging(struct page *page) > } > > void mte_zero_clear_page_tags(void *addr); > -void mte_sync_tags(pte_t old_pte, pte_t pte); > +void mte_sync_tags(pte_t pte); > void mte_copy_page_tags(void *kto, const void *kfrom); > void mte_thread_init_user(void); > void mte_thread_switch(struct task_struct *next); > @@ -122,7 +122,7 @@ static inline bool try_page_mte_tagging(struct page *page) > static inline void mte_zero_clear_page_tags(void *addr) > { > } > -static inline void mte_sync_tags(pte_t old_pte, pte_t pte) > +static inline void mte_sync_tags(pte_t pte) > { > } > static inline void mte_copy_page_tags(void *kto, const void *kfrom) > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index 0bd18de9fd97..e8a252e62b12 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -337,18 +337,8 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr, > * don't expose tags (instruction fetches don't check tags). > */ > if (system_supports_mte() && pte_access_permitted(pte, false) && > - !pte_special(pte)) { > - pte_t old_pte = READ_ONCE(*ptep); > - /* > - * We only need to synchronise if the new PTE has tags enabled > - * or if swapping in (in which case another mapping may have > - * set tags in the past even if this PTE isn't tagged). > - * (!pte_none() && !pte_present()) is an open coded version of > - * is_swap_pte() > - */ > - if (pte_tagged(pte) || (!pte_none(old_pte) && !pte_present(old_pte))) > - mte_sync_tags(old_pte, pte); > - } > + !pte_special(pte) && pte_tagged(pte)) > + mte_sync_tags(pte); > > __check_safe_pte_update(mm, ptep, pte); > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index 7e89968bd282..c40728046fed 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -35,41 +35,18 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); > EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode); > #endif > > -static void mte_sync_page_tags(struct page *page, pte_t old_pte, > - bool check_swap, bool pte_is_tagged) > -{ > - if (check_swap && is_swap_pte(old_pte)) { > - swp_entry_t entry = pte_to_swp_entry(old_pte); > - > - if (!non_swap_entry(entry)) > - mte_restore_tags(entry, page); > - } > - > - if (!pte_is_tagged) > - return; > - > - if (try_page_mte_tagging(page)) { > - mte_clear_page_tags(page_address(page)); > - set_page_mte_tagged(page); > - } > -} > - > -void mte_sync_tags(pte_t old_pte, pte_t pte) > +void mte_sync_tags(pte_t pte) > { > struct page *page = pte_page(pte); > long i, nr_pages = compound_nr(page); > - bool check_swap = nr_pages == 1; > - bool pte_is_tagged = pte_tagged(pte); > - > - /* Early out if there's nothing to do */ > - if (!check_swap && !pte_is_tagged) > - return; > > /* if PG_mte_tagged is set, tags have already been initialised */ > - for (i = 0; i < nr_pages; i++, page++) > - if (!page_mte_tagged(page)) > - mte_sync_page_tags(page, old_pte, check_swap, > - pte_is_tagged); > + for (i = 0; i < nr_pages; i++, page++) { > + if (try_page_mte_tagging(page)) { > + mte_clear_page_tags(page_address(page)); > + set_page_mte_tagged(page); > + } > + } > > /* ensure the tags are visible before the PTE is set */ > smp_wmb(); > diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c > index cd508ba80ab1..3a78bf1b1364 100644 > --- a/arch/arm64/mm/mteswap.c > +++ b/arch/arm64/mm/mteswap.c > @@ -53,10 +53,9 @@ void mte_restore_tags(swp_entry_t entry, struct page *page) > if (!tags) > return; > > - if (try_page_mte_tagging(page)) { > - mte_restore_page_tags(page_address(page), tags); > - set_page_mte_tagged(page); > - } > + WARN_ON_ONCE(!try_page_mte_tagging(page)); > + mte_restore_page_tags(page_address(page), tags); > + set_page_mte_tagged(page); > } > > void mte_invalidate_tags(int type, pgoff_t offset)
