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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qfvUj-005c9Y-MQ; Tue, 12 Sep 2023 04:59:25 +0000 Date: Tue, 12 Sep 2023 05:59:25 +0100 From: Matthew Wilcox To: Dave Hansen Cc: Yin Fengwei , syzbot , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [mm?] BUG: Bad page map (7) Message-ID: References: <000000000000d099fa0604f03351@google.com> <0465d13d-83b6-163d-438d-065d03e9ba76@intel.com> <092a9bb2-727e-5849-fa4f-18535b998efc@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <092a9bb2-727e-5849-fa4f-18535b998efc@intel.com> X-Rspamd-Queue-Id: 9A4824000A X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: hjp33x7ru6c315urckfegahudzsb6sim X-HE-Tag: 1694494773-677636 X-HE-Meta: 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 JA4JkkA1 xUyVoBwIhCCcE2CqMLYE8A6qS30k0q61axtbHi1XskpL+QoaTWZp6k3MOYhGETqkziPgZo62jqG6T0zFAnoaACtTpCSLMrJJeBW3PvUzEJsFzCdzLKvLB4adGSXChgW0AzZJWJoZ/b4c5MwAxVtOHwM2G0qSo0DN9mWayX5rWw9OwJQWVhVnvfAaTjR37gfa3k8HfMKnzwgJ5Y7ydDyOLYPp5y2Yw/LuoylGmUK2YRbIk+lBpKekI54bbJFZe5tL3wVqzrC2bSmW12r7b/ZSxYojq5w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 11, 2023 at 01:22:51PM -0700, Dave Hansen wrote: > On 9/11/23 12:12, Matthew Wilcox wrote: > > On Mon, Sep 11, 2023 at 09:55:37AM -0700, Dave Hansen wrote: > >> On 9/11/23 09:44, Matthew Wilcox wrote: > >>> After fixing your two typos, this assembles to 176 bytes more code than > >>> my version. Not sure that's great. > >> Maybe I'm a fool, but 176 bytes of text bloat isn't scaring me off too > >> much. I'd much rather have that than another window into x86 goofiness > >> to maintain. > >> > >> Does that 176 bytes translate into meaningful performance, or is it just > >> a bunch of register bit twiddling that the CPU will sail through? > > I'm ... not sure how to tell. It's 1120 bytes vs 944 bytes and crawling > > through that much x86 assembly isn't my idea of a great time. I can > > send you objdump -dr for all three options if you like? Maybe there's > > a quick way to compare them that I've never known about. > > Working patches would be great if you're got 'em handy, plus your > .config and generally what compiler you're on. gcc (Debian 13.2.0-2) 13.2.0 I don't think there's anything particularly strange about my .config If you compile this patch as-is, you'll get your preferred code. Remove the #define DH and you get mine. I would say that 176 bytes is 3 cachelines of I$, which isn't free, even if all the insns in it can be executed while the CPU is waiting for cache misses. This ought to be a pretty tight loop anyway; we're just filling in adjacent PTEs. There may not be many spare cycles for "free" uops to execute. diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index d6ad98ca1288..c9781b8b14af 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -955,6 +955,14 @@ static inline int pte_same(pte_t a, pte_t b) return a.pte == b.pte; } +static inline pte_t pte_next(pte_t pte) +{ + if (__pte_needs_invert(pte_val(pte))) + return __pte(pte_val(pte) - (1UL << PFN_PTE_SHIFT)); + return __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT)); +} +#define pte_next pte_next + static inline int pte_present(pte_t a) { return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE); diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 1fba072b3dac..25333cf3c865 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -205,6 +205,10 @@ static inline int pmd_young(pmd_t pmd) #define arch_flush_lazy_mmu_mode() do {} while (0) #endif +#ifndef pte_next +#define pte_next(pte) ((pte) + (1UL << PFN_PTE_SHIFT)) +#endif + #ifndef set_ptes /** * set_ptes - Map consecutive pages to a contiguous range of addresses. @@ -223,6 +227,11 @@ static inline int pmd_young(pmd_t pmd) static inline void set_ptes(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte, unsigned int nr) { +#define DH +#ifdef DH + pgprot_t prot = pte_pgprot(pte); + unsigned long pfn = pte_pfn(pte); +#endif page_table_check_ptes_set(mm, ptep, pte, nr); arch_enter_lazy_mmu_mode(); @@ -231,7 +240,12 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr, if (--nr == 0) break; ptep++; - pte = __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT)); +#ifdef DH + pfn++; + pte = pfn_pte(pfn, prot); +#else + pte = pte_next(pte); +#endif } arch_leave_lazy_mmu_mode(); }