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mm: call wp_page_copy() under the VMA lock 

It is usually safe to call wp_page_copy() under the VMA lock.  The only
unsafe situation is when no anon_vma has been allocated for this VMA, and
we have to look at adjacent VMAs to determine if their anon_vma can be
shared.  Since this happens only for the first COW of a page in this VMA,
the majority of calls to wp_page_copy() do not need to fall back to the
mmap_sem.

Add vmf_anon_prepare() as an alternative to anon_vma_prepare() which will
return RETRY if we currently hold the VMA lock and need to allocate an
anon_vma.  This lets us drop the check in do_wp_page().

Link: https://lkml.kernel.org/r/20231006195318.4087158-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-10-06 20:53:14 +01:00 committed by Andrew Morton
parent 5d74b2ab2c
commit 164b06f238
1 changed files with 26 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
mm/memory.c
View File

@ -3042,6 +3042,21 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
count_vm_event(PGREUSE);
}
static vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
if (likely(vma->anon_vma))
return 0;
if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
vma_end_read(vma);
return VM_FAULT_RETRY;
}
if (__anon_vma_prepare(vma))
return VM_FAULT_OOM;
return 0;
}
/*
* Handle the case of a page which we actually need to copy to a new page,
* either due to COW or unsharing.
@ -3069,27 +3084,29 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
pte_t entry;
int page_copied = 0;
struct mmu_notifier_range range;
int ret;
vm_fault_t ret;
delayacct_wpcopy_start();
if (vmf->page)
old_folio = page_folio(vmf->page);
if (unlikely(anon_vma_prepare(vma)))
goto oom;
ret = vmf_anon_prepare(vmf);
if (unlikely(ret))
goto out;
if (is_zero_pfn(pte_pfn(vmf->orig_pte))) {
new_folio = vma_alloc_zeroed_movable_folio(vma, vmf->address);
if (!new_folio)
goto oom;
} else {
int err;
new_folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma,
vmf->address, false);
if (!new_folio)
goto oom;
ret = __wp_page_copy_user(&new_folio->page, vmf->page, vmf);
if (ret) {
err = __wp_page_copy_user(&new_folio->page, vmf->page, vmf);
if (err) {
/*
* COW failed, if the fault was solved by other,
* it's fine. If not, userspace would re-fault on
@ -3102,7 +3119,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
folio_put(old_folio);
delayacct_wpcopy_end();
return ret == -EHWPOISON ? VM_FAULT_HWPOISON : 0;
return err == -EHWPOISON ? VM_FAULT_HWPOISON : 0;
}
kmsan_copy_page_meta(&new_folio->page, vmf->page);
}
@ -3212,11 +3229,13 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
oom_free_new:
folio_put(new_folio);
oom:
ret = VM_FAULT_OOM;
out:
if (old_folio)
folio_put(old_folio);
delayacct_wpcopy_end();
return VM_FAULT_OOM;
return ret;
}
/**
@ -3458,12 +3477,6 @@ reuse:
return 0;
}
copy:
if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma->anon_vma) {
pte_unmap_unlock(vmf->pte, vmf->ptl);
vma_end_read(vmf->vma);
return VM_FAULT_RETRY;
}
/*
* Ok, we need to copy. Oh, well..
*/