Re: [PATCH v3] mmu_gather: move tlb flush for VM_PFNMAP/VM_MIXEDMAP vmas into free_pgtables()

[Roman Gushchin <roman.gushchin@linux.dev>]

On Thu, Jan 23, 2025 at 02:42:56PM -0500, Liam R. Howlett wrote:
> * Roman Gushchin <roman.gushchin@linux.dev> [250123 11:44]:
> > Commit b67fbebd4cf9 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas")
> > added a forced tlbflush to tlb_vma_end(), which is required to avoid a
> > race between munmap() and unmap_mapping_range(). However it added some
> > overhead to other paths where tlb_vma_end() is used, but vmas are not
> > removed, e.g. madvise(MADV_DONTNEED).
> > 
> > Fix this by moving the tlb flush out of tlb_end_vma() into
> > free_pgtables(), somewhat similar to the stable version of the
> > original commit: e.g. stable commit 895428ee124a ("mm: Force TLB flush
> > for PFNMAP mappings before unlink_file_vma()").
> > 
> > Note, that if tlb->fullmm is set, no flush is required, as the whole
> > mm is about to be destroyed.
> > 
> > ---
> 
> Hugh didn't mean to add a ---, he meant to move the version info between
> the Cc list and the patch so that it's not in the git history.

Ah, ok, somehow it wasn't a problem previously for me, usually Andrew
was dropping the part while merging into the mm tree.
Thanks for clarifying.

> 
> You can find examples on the ML.
> 
> > 
> > v3:
> >   - added initialization of vma_pfn in __tlb_reset_range() (by Hugh D.)
> > 
> > v2:
> >   - moved vma_pfn flag handling into tlb.h (by Peter Z.)
> >   - added comments (by Peter Z.)
> >   - fixed the vma_pfn flag setting (by Hugh D.)
> > 
> 
> 
> > Suggested-by: Jann Horn <jannh@google.com>
> > Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
> 
> Link: some email discussion url lore.kernel.org..

It was based on some non-public discussion unfortunately, so no lore link.

Thank you!