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Message-ID: <ZOcC7RsYy5yJLgNb@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Thu, 24 Aug 2023 09:12:45 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Kefeng Wang <wangkefeng.wang@...wei.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
surenb@...gle.com, willy@...radead.org,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Huacai Chen <chenhuacai@...nel.org>,
WANG Xuerui <kernel@...0n.name>,
Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org,
linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH rfc v2 01/10] mm: add a generic VMA lock-based page fault
handler
On Mon, Aug 21, 2023 at 08:30:47PM +0800, Kefeng Wang wrote:
Hi Kefeng,
> The ARCH_SUPPORTS_PER_VMA_LOCK are enabled by more and more architectures,
> eg, x86, arm64, powerpc and s390, and riscv, those implementation are very
> similar which results in some duplicated codes, let's add a generic VMA
> lock-based page fault handler try_to_vma_locked_page_fault() to eliminate
> them, and which also make us easy to support this on new architectures.
>
> Since different architectures use different way to check vma whether is
> accessable or not, the struct pt_regs, page fault error code and vma flags
> are added into struct vm_fault, then, the architecture's page fault code
> could re-use struct vm_fault to record and check vma accessable by each
> own implementation.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
> include/linux/mm.h | 17 +++++++++++++++++
> include/linux/mm_types.h | 2 ++
> mm/memory.c | 39 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 58 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 3f764e84e567..22a6f4c56ff3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -512,9 +512,12 @@ struct vm_fault {
> pgoff_t pgoff; /* Logical page offset based on vma */
> unsigned long address; /* Faulting virtual address - masked */
> unsigned long real_address; /* Faulting virtual address - unmasked */
> + unsigned long fault_code; /* Faulting error code during page fault */
> + struct pt_regs *regs; /* The registers stored during page fault */
> };
> enum fault_flag flags; /* FAULT_FLAG_xxx flags
> * XXX: should really be 'const' */
> + vm_flags_t vm_flags; /* VMA flags to be used for access checking */
> pmd_t *pmd; /* Pointer to pmd entry matching
> * the 'address' */
> pud_t *pud; /* Pointer to pud entry matching
> @@ -774,6 +777,9 @@ static inline void assert_fault_locked(struct vm_fault *vmf)
> struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
> unsigned long address);
>
> +bool arch_vma_access_error(struct vm_area_struct *vma, struct vm_fault *vmf);
> +vm_fault_t try_vma_locked_page_fault(struct vm_fault *vmf);
> +
> #else /* CONFIG_PER_VMA_LOCK */
>
> static inline bool vma_start_read(struct vm_area_struct *vma)
> @@ -801,6 +807,17 @@ static inline void assert_fault_locked(struct vm_fault *vmf)
> mmap_assert_locked(vmf->vma->vm_mm);
> }
>
> +static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
> + unsigned long address)
> +{
> + return NULL;
> +}
> +
> +static inline vm_fault_t try_vma_locked_page_fault(struct vm_fault *vmf)
> +{
> + return VM_FAULT_NONE;
> +}
> +
> #endif /* CONFIG_PER_VMA_LOCK */
>
> extern const struct vm_operations_struct vma_dummy_vm_ops;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index f5ba5b0bc836..702820cea3f9 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -1119,6 +1119,7 @@ typedef __bitwise unsigned int vm_fault_t;
> * fault. Used to decide whether a process gets delivered SIGBUS or
> * just gets major/minor fault counters bumped up.
> *
> + * @VM_FAULT_NONE: Special case, not starting to handle fault
> * @VM_FAULT_OOM: Out Of Memory
> * @VM_FAULT_SIGBUS: Bad access
> * @VM_FAULT_MAJOR: Page read from storage
> @@ -1139,6 +1140,7 @@ typedef __bitwise unsigned int vm_fault_t;
> *
> */
> enum vm_fault_reason {
> + VM_FAULT_NONE = (__force vm_fault_t)0x000000,
> VM_FAULT_OOM = (__force vm_fault_t)0x000001,
> VM_FAULT_SIGBUS = (__force vm_fault_t)0x000002,
> VM_FAULT_MAJOR = (__force vm_fault_t)0x000004,
> diff --git a/mm/memory.c b/mm/memory.c
> index 3b4aaa0d2fff..60fe35db5134 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5510,6 +5510,45 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
> count_vm_vma_lock_event(VMA_LOCK_ABORT);
> return NULL;
> }
> +
> +#ifdef CONFIG_PER_VMA_LOCK
> +bool __weak arch_vma_access_error(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> + return (vma->vm_flags & vmf->vm_flags) == 0;
> +}
> +#endif
> +
> +vm_fault_t try_vma_locked_page_fault(struct vm_fault *vmf)
> +{
> + vm_fault_t fault = VM_FAULT_NONE;
> + struct vm_area_struct *vma;
> +
> + if (!(vmf->flags & FAULT_FLAG_USER))
> + return fault;
> +
> + vma = lock_vma_under_rcu(current->mm, vmf->real_address);
> + if (!vma)
> + return fault;
> +
> + if (arch_vma_access_error(vma, vmf)) {
> + vma_end_read(vma);
> + return fault;
> + }
> +
> + fault = handle_mm_fault(vma, vmf->real_address,
> + vmf->flags | FAULT_FLAG_VMA_LOCK, vmf->regs);
> +
> + if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
> + vma_end_read(vma);
Could you please explain how vma_end_read() call could be conditional?
> +
> + if (fault & VM_FAULT_RETRY)
> + count_vm_vma_lock_event(VMA_LOCK_RETRY);
> + else
> + count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
> +
> + return fault;
> +}
> +
> #endif /* CONFIG_PER_VMA_LOCK */
>
> #ifndef __PAGETABLE_P4D_FOLDED
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