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Message-ID: <1624be86-4c17-46e5-fafc-eb8afb7b9b4a@linux.ibm.com>
Date: Tue, 6 Sep 2022 16:26:54 +0200
From: Laurent Dufour <ldufour@...ux.ibm.com>
To: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc: michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
vbabka@...e.cz, hannes@...xchg.org, mgorman@...e.de,
dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
peterz@...radead.org, laurent.dufour@...ibm.com,
paulmck@...nel.org, luto@...nel.org, songliubraving@...com,
peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
rientjes@...gle.com, axelrasmussen@...gle.com, joelaf@...gle.com,
minchan@...gle.com, kernel-team@...roid.com, linux-mm@...ck.org,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND 06/28] mm: mark VMA as locked whenever
vma->vm_flags are modified
Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :
> VMA flag modifications should be done under VMA lock to prevent concurrent
> page fault handling in that area.
>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
> fs/proc/task_mmu.c | 1 +
> fs/userfaultfd.c | 6 ++++++
> mm/madvise.c | 1 +
> mm/mlock.c | 2 ++
> mm/mmap.c | 1 +
> mm/mprotect.c | 1 +
> 6 files changed, 12 insertions(+)
There are few changes also done in the driver's space, for instance:
*** arch/x86/kernel/cpu/sgx/driver.c:
sgx_mmap[98] vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND |
VM_DONTDUMP | VM_IO;
*** arch/x86/kernel/cpu/sgx/virt.c:
sgx_vepc_mmap[108] vma->vm_flags |= VM_PFNMAP | VM_IO |
VM_DONTDUMP | VM_DONTCOPY;
*** drivers/dax/device.c:
dax_mmap[311] vma->vm_flags |= VM_HUGEPAGE;
I guess these changes to vm_flags should be protected as well, or to be
checked one by one.
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 4e0023643f8b..ceffa5c2c650 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1285,6 +1285,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> for (vma = mm->mmap; vma; vma = vma->vm_next) {
> if (!(vma->vm_flags & VM_SOFTDIRTY))
> continue;
> + vma_mark_locked(vma);
> vma->vm_flags &= ~VM_SOFTDIRTY;
> vma_set_page_prot(vma);
> }
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 175de70e3adf..fe557b3d1c07 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -620,6 +620,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
> mmap_write_lock(mm);
> for (vma = mm->mmap; vma; vma = vma->vm_next)
> if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
> + vma_mark_locked(vma);
> vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> vma->vm_flags &= ~__VM_UFFD_FLAGS;
> }
> @@ -653,6 +654,7 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
>
> octx = vma->vm_userfaultfd_ctx.ctx;
> if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
> + vma_mark_locked(vma);
> vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> vma->vm_flags &= ~__VM_UFFD_FLAGS;
> return 0;
> @@ -734,6 +736,7 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
> atomic_inc(&ctx->mmap_changing);
> } else {
> /* Drop uffd context if remap feature not enabled */
> + vma_mark_locked(vma);
> vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> vma->vm_flags &= ~__VM_UFFD_FLAGS;
> }
> @@ -891,6 +894,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> vma = prev;
> else
> prev = vma;
> + vma_mark_locked(vma);
> vma->vm_flags = new_flags;
> vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
> }
> @@ -1449,6 +1453,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> * the next vma was merged into the current one and
> * the current one has not been updated yet.
> */
> + vma_mark_locked(vma);
> vma->vm_flags = new_flags;
> vma->vm_userfaultfd_ctx.ctx = ctx;
>
> @@ -1630,6 +1635,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> * the next vma was merged into the current one and
> * the current one has not been updated yet.
> */
> + vma_mark_locked(vma);
> vma->vm_flags = new_flags;
> vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 5f0f0948a50e..a173f0025abd 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -181,6 +181,7 @@ static int madvise_update_vma(struct vm_area_struct *vma,
> /*
> * vm_flags is protected by the mmap_lock held in write mode.
> */
> + vma_mark_locked(vma);
> vma->vm_flags = new_flags;
> if (!vma->vm_file) {
> error = replace_anon_vma_name(vma, anon_name);
> diff --git a/mm/mlock.c b/mm/mlock.c
> index b14e929084cc..f62e1a4d05f2 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -380,6 +380,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
> */
> if (newflags & VM_LOCKED)
> newflags |= VM_IO;
> + vma_mark_locked(vma);
> WRITE_ONCE(vma->vm_flags, newflags);
>
> lru_add_drain();
> @@ -456,6 +457,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
>
> if ((newflags & VM_LOCKED) && (oldflags & VM_LOCKED)) {
> /* No work to do, and mlocking twice would be wrong */
> + vma_mark_locked(vma);
> vma->vm_flags = newflags;
> } else {
> mlock_vma_pages_range(vma, start, end, newflags);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 693e6776be39..f89c9b058105 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1818,6 +1818,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> out:
> perf_event_mmap(vma);
>
> + vma_mark_locked(vma);
> vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
> if (vm_flags & VM_LOCKED) {
> if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
I guess, this doesn't really impact, but the call to vma_mark_locked(vma)
may be done only in the case the vm_flags field is touched.
Something like this:
vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
if (vm_flags & VM_LOCKED) {
if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
is_vm_hugetlb_page(vma) ||
- vma == get_gate_vma(current->mm))
+ vma == get_gate_vma(current->mm)) {
+ vma_mark_locked(vma);
vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
- else
+ } else
mm->locked_vm += (len >> PAGE_SHIFT);
}
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index bc6bddd156ca..df47fc21b0e4 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -621,6 +621,7 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma,
> * vm_flags and vm_page_prot are protected by the mmap_lock
> * held in write mode.
> */
> + vma_mark_locked(vma);
> vma->vm_flags = newflags;
> /*
> * We want to check manually if we can change individual PTEs writable
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