linux-kernel - Re: [PATCH v6 01/26] fuse: Fix dax truncate/punch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <67a5111b2f805_2d2c29448@dwillia2-xfh.jf.intel.com.notmuch>
Date: Thu, 6 Feb 2025 11:44:27 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Asahi Lina <lina@...hilina.net>, Dan Williams <dan.j.williams@...el.com>,
	Vivek Goyal <vgoyal@...hat.com>, Alistair Popple <apopple@...dia.com>
CC: <akpm@...ux-foundation.org>, <dan.j.williams@...el.com>,
	<linux-mm@...ck.org>, <alison.schofield@...el.com>, <zhang.lyra@...il.com>,
	<gerald.schaefer@...ux.ibm.com>, <vishal.l.verma@...el.com>,
	<dave.jiang@...el.com>, <logang@...tatee.com>, <bhelgaas@...gle.com>,
	<jack@...e.cz>, <jgg@...pe.ca>, <catalin.marinas@....com>, <will@...nel.org>,
	<mpe@...erman.id.au>, <npiggin@...il.com>, <dave.hansen@...ux.intel.com>,
	<ira.weiny@...el.com>, <willy@...radead.org>, <djwong@...nel.org>,
	<tytso@....edu>, <linmiaohe@...wei.com>, <david@...hat.com>,
	<peterx@...hat.com>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <nvdimm@...ts.linux.dev>,
	<linux-cxl@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-ext4@...r.kernel.org>, <linux-xfs@...r.kernel.org>,
	<jhubbard@...dia.com>, <hch@....de>, <david@...morbit.com>,
	<chenhuacai@...nel.org>, <kernel@...0n.name>, <loongarch@...ts.linux.dev>,
	Hanna Czenczek <hreitz@...hat.com>, German Maglione <gmaglione@...hat.com>
Subject: Re: [PATCH v6 01/26] fuse: Fix dax truncate/punch_hole fault path

Asahi Lina wrote:
> Hi,
> 
> On February 6, 2025 1:10:15 AM GMT+01:00, Dan Williams <dan.j.williams@...el.com> wrote:
> >Vivek Goyal wrote:
> >> On Fri, Jan 10, 2025 at 05:00:29PM +1100, Alistair Popple wrote:
> >> > FS DAX requires file systems to call into the DAX layout prior to unlinking
> >> > inodes to ensure there is no ongoing DMA or other remote access to the
> >> > direct mapped page. The fuse file system implements
> >> > fuse_dax_break_layouts() to do this which includes a comment indicating
> >> > that passing dmap_end == 0 leads to unmapping of the whole file.
> >> > 
> >> > However this is not true - passing dmap_end == 0 will not unmap anything
> >> > before dmap_start, and further more dax_layout_busy_page_range() will not
> >> > scan any of the range to see if there maybe ongoing DMA access to the
> >> > range. Fix this by passing -1 for dmap_end to fuse_dax_break_layouts()
> >> > which will invalidate the entire file range to
> >> > dax_layout_busy_page_range().
> >> 
> >> Hi Alistair,
> >> 
> >> Thanks for fixing DAX related issues for virtiofs. I am wondering how are
> >> you testing DAX with virtiofs. AFAIK, we don't have DAX support in Rust
> >> virtiofsd. C version of virtiofsd used to have out of the tree patches
> >> for DAX. But C version got deprecated long time ago.
> >> 
> >> Do you have another implementation of virtiofsd somewhere else which
> >> supports DAX and allows for testing DAX related changes?
> >
> >I have personally never seen a virtiofs-dax test. It sounds like you are
> >saying we can deprecate that support if there are no longer any users.
> >Or, do you expect that C-virtiofsd is alive in the ecosystem?
> 
> I accidentally replied offlist, but I wanted to mention that libkrun
> supports DAX and we use it in muvm. It's a critical part of x11bridge
> functionality, since it uses DAX to share X11 shm fences between X11
> clients in the VM and the XWayland server on the host, which only
> works if the mmaps are coherent.

Ah, good to hear. It would be lovely to integrate an muvm smoketest
somewhere in https://github.com/pmem/ndctl/tree/main/test so that we
have early warning on potential breakage.