Re: [PATCH v3 4/7] arm64: mte: Lock a page for MTE tag initialisation
From: Steven Price <steven.price@arm.com>
Date: 2022-09-05 09:26:28
Also in:
kvm, kvmarm
On 02/09/2022 17:58, Catalin Marinas wrote:
On Fri, Sep 02, 2022 at 05:28:47PM +0100, Catalin Marinas wrote:quoted
On Fri, Sep 02, 2022 at 03:47:33PM +0100, Steven Price wrote:quoted
On 10/08/2022 20:30, Peter Collingbourne wrote:quoted
diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c index a78c1db23c68..cd5ad0936e16 100644 --- a/arch/arm64/mm/mteswap.c +++ b/arch/arm64/mm/mteswap.c@@ -53,6 +53,9 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page) if (!tags) return false; + /* racing tag restoring? */ + if (!try_page_mte_tagging(page)) + return false; mte_restore_page_tags(page_address(page), tags);I feel like adding a "set_page_mte_tagged(page);" in here would avoid the need for the comments about mte_restore_tags() taking the lock.Good point. I think I blindly followed the set_bit() places but it makes sense to move the bit setting to mte_restore_tags().Something like this (and I need to do some more testing):
Exactly, that looks equivalent and is hopefully easier to follow. Steve
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index b956899467f0..be6560e1ff2b 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h@@ -25,7 +25,7 @@ unsigned long mte_copy_tags_to_user(void __user *to, void *from, unsigned long n); int mte_save_tags(struct page *page); void mte_save_page_tags(const void *page_addr, void *tag_storage); -bool mte_restore_tags(swp_entry_t entry, struct page *page); +void mte_restore_tags(swp_entry_t entry, struct page *page); void mte_restore_page_tags(void *page_addr, const void *tag_storage); void mte_invalidate_tags(int type, pgoff_t offset); void mte_invalidate_tags_area(int type);diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index e6b82ad1e9e6..7d91379382fd 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h@@ -1049,9 +1049,8 @@ static inline void arch_swap_invalidate_area(int type) #define __HAVE_ARCH_SWAP_RESTORE static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio) { - /* mte_restore_tags() takes the PG_mte_lock */ - if (system_supports_mte() && mte_restore_tags(entry, &folio->page)) - set_page_mte_tagged(&folio->page); + if (system_supports_mte()) + mte_restore_tags(entry, &folio->page); } #endif /* CONFIG_ARM64_MTE */diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index 634e089b5933..54ab6c4741db 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c@@ -41,11 +41,8 @@ static void mte_sync_page_tags(struct page *page, pte_t old_pte, if (check_swap && is_swap_pte(old_pte)) { swp_entry_t entry = pte_to_swp_entry(old_pte); - /* mte_restore_tags() takes the PG_mte_lock */ - if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) { - set_page_mte_tagged(page); - return; - } + if (!non_swap_entry(entry)) + mte_restore_tags(entry, page); } if (!pte_is_tagged)diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c index cd5ad0936e16..cd508ba80ab1 100644 --- a/arch/arm64/mm/mteswap.c +++ b/arch/arm64/mm/mteswap.c@@ -46,19 +46,17 @@ int mte_save_tags(struct page *page) return 0; } -bool mte_restore_tags(swp_entry_t entry, struct page *page) +void mte_restore_tags(swp_entry_t entry, struct page *page) { void *tags = xa_load(&mte_pages, entry.val); if (!tags) - return false; + return; - /* racing tag restoring? */ - if (!try_page_mte_tagging(page)) - return false; - mte_restore_page_tags(page_address(page), tags); - - return true; + if (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)
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