From: Keith Busch <kbusch@kernel.org>
To: Ben Copeland <ben.copeland@linaro.org>
Cc: Christoph Hellwig <hch@lst.de>,
linux-kernel@vger.kernel.org, lkft-triage@lists.linaro.org,
regressions@lists.linux.dev, linux-nvme@lists.infradead.org,
Dan Carpenter <dan.carpenter@linaro.org>,
axboe@kernel.dk, sagi@grimberg.me, iommu@lists.linux.dev
Subject: Re: next-20250627: IOMMU DMA warning during NVMe I/O completion after 06cae0e3f61c
Date: Tue, 1 Jul 2025 15:43:54 -0400 [thread overview]
Message-ID: <aGQ6eiL22KIMjSGo@kbusch-mbp> (raw)
In-Reply-To: <CAL0q8a7sE4a00ehKrkyepA_xA3Z2HiGv0LazvYe=2NciTkkPFQ@mail.gmail.com>
On Mon, Jun 30, 2025 at 08:51:01PM +0100, Ben Copeland wrote:
>
> [ 1.083447] arm-smmu-v3 arm-smmu-v3.16.auto: option mask 0x0
> [ 1.083460] arm-smmu-v3 arm-smmu-v3.16.auto: IDR0.HTTU features(0x600000) overridden by FW configuration (0x0)
> [ 1.083463] arm-smmu-v3 arm-smmu-v3.16.auto: ias 48-bit, oas 48-bit (features 0x0094dfef)
Neat, I have machine with the same. The iommu granularity appears to be
able to take on various values, so let's see what the iommu group's
pgsize_bitmap is on mine with some bpf and drgn magic:
# bpftrace -e 'kfunc:iommu_group_show_type { printf("iommu_group: 0x%lx\n", args->group); }' &
# cat /sys/kernel/iommu_groups/0/type
iommu_group: 0xffff0000b54d0600
# drgn
>>> hex(Object(prog, "struct iommu_group *", 0xffff0000b54d0600).default_domain.pgsize_bitmap)
'0x20010000'
So 64k is the minimum iommu granularity in its current configuration.
Definitely too big to guarantee coalescing nvme segments, so if yours is
similarly configured, that explains why it takes the path you're taking.
next prev parent reply other threads:[~2025-07-01 19:43 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20250630075218epcas5p1f3d467fffa468cac0ccd012c193e94df@epcas5p1.samsung.com>
2025-06-30 7:50 ` next-20250627: IOMMU DMA warning during NVMe I/O completion after 06cae0e3f61c Ben Copeland
2025-06-30 13:33 ` Christoph Hellwig
2025-06-30 19:51 ` Ben Copeland
2025-07-01 19:43 ` Keith Busch [this message]
2025-06-30 20:25 ` Keith Busch
2025-07-01 0:54 ` Keith Busch
2025-07-01 13:05 ` Ben Copeland
2025-07-01 14:20 ` Keith Busch
2025-07-01 13:29 ` Christoph Hellwig
2025-07-01 15:58 ` Leon Romanovsky
2025-07-01 21:00 ` Keith Busch
2025-07-03 9:30 ` Christoph Hellwig
2025-07-03 14:29 ` Keith Busch
2025-07-03 15:13 ` Ben Copeland
2025-07-03 5:54 ` Kanchan Joshi
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