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Howlett" , Ryan Roberts Subject: Re: [PATCH] vfio: Request THP-aligned mmap for device fds Message-ID: References: <20260616180129.160016-1-anthony.pighin@nokia.com> <20260616163054.77fdb61a@shazbot.org> <20260617192928.GB231643@ziepe.ca> <20260618153049.GG231643@ziepe.ca> <20260619131658.GA1068655@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260619131658.GA1068655@ziepe.ca> X-Rspam-User: X-Stat-Signature: 357ra9s1hztmphdb4gb7bxpyuhfgrsok X-Rspamd-Queue-Id: C48CB1C0010 X-Rspamd-Server: rspam11 X-HE-Tag: 1782147257-542574 X-HE-Meta: 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 xGqjye7S QaV50VdcjppklGVQ89RpGmwedfilDN/vNFROv+D42wLgjDEX29/qDPHkiQsqdebVdM8JdG8Uc1VrwON9rxUuHg47UL4Jnr7cl5lFtXYy1PnFNwweyNZ/01sx9MCQDNVS++aRwcrR/9KfzY+n/FVLcvx+cjT0iPpmAgwTy6crH3V4Mvmf4OqagQYHn5EukbRhlMT5AoxBEjwlPV9/k5714W+BEKhLttUwnTDMm0/JAX36ohXF4W+2n9Jp8mTlcEL0ztXHiSlC+G4JExQUIqpjuv6kgFrvTjdnJE0YZ7jgJS5fl32XBdC92E7wOU8cw4BZaS8QWPNye1BUSbRM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 19, 2026 at 10:16:58AM -0300, Jason Gunthorpe wrote: > On Thu, Jun 18, 2026 at 04:56:06PM +0100, Lorenzo Stoakes wrote: > > > > What you're saying is that offset 0 of the opened file might correspond > > > > to a PFN that is not aligned in any way? I had assumed that when trying > > > > to do the mapping of (2MB+4KiB to 64MB), that the offset specified to > > > > mmap was 2MB+4KiB. But you seem to be saying that the offset in that > > > > case would be 0 and someone needs to know that it corresponds to a PFN > > > > that is misaligned? > > > > > > I do expect that the pgoff space is usually aligned to the pfn space, > > > most drivers do that or could be improved to do that. There will be > > > some off cases, but maybe we don't care, and VFIO should be fine. > > > > Some stuff has weird assumptions about pfn=0 at start of the range (DMA for > > instance). > > Do you have a pointer? I'm drawing a blank what "dma" is? (I am obliged to link https://xkcd.com/138/... :) dmabuf as in [0], where vma->vm_pgoff must be the page offset into the DMA buffer. [0]:https://elixir.bootlin.com/linux/v7.1/source/kernel/dma/direct.c#L550 > > Jason Thanks, Lorenzo