From: Will Deacon <will@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Robin Murphy <robin.murphy@arm.com>,
Tyler Hicks <code@tyhicks.com>,
Jerry Snitselaar <jsnitsel@redhat.com>,
linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org, Dexuan Cui <decui@microsoft.com>,
Easwar Hariharan <eahariha@linux.microsoft.com>
Subject: Re: Why is the ARM SMMU v1/v2 put into bypass mode on kexec?
Date: Fri, 22 Mar 2024 15:55:29 +0000 [thread overview]
Message-ID: <20240322155529.GE5634@willie-the-truck> (raw)
In-Reply-To: <20240319175007.GC66976@ziepe.ca>
Hey Jason,
On Tue, Mar 19, 2024 at 02:50:07PM -0300, Jason Gunthorpe wrote:
> On Tue, Mar 19, 2024 at 03:47:56PM +0000, Will Deacon wrote:
>
> > Right, it's hard to win if DMA-active devices weren't quiesced properly
> > by the outgoing kernel. Either the SMMU was left in abort (leading to the
> > problems you list above) or the SMMU is left in bypass (leading to possible
> > data corruption). Which is better?
>
> For whatever reason (and I really don't like this design) alot of work
> was done on x86 so that device continues to work as-was right up until
> the crash kernel does the first DMA operation. Including having the
> crash kernel non disruptively inherit and retain the IOMMU
> configuration. (eg see translation_pre_enabled() stuff in intel
> driver)
Right, I'm also not thrilled about trying to implement that :)
What we have at the moment seems to be good enough to avoid folks
complaining about it.
For the case Tyler is reporting, though, I _think_ it's just a standard
kexec() rather than a crashkernel.
Will
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next prev parent reply other threads:[~2024-03-22 15:55 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-14 7:49 Why is the ARM SMMU v1/v2 put into bypass mode on kexec? Tyler Hicks
2024-03-14 19:06 ` Tyler Hicks
2024-03-19 12:57 ` Robin Murphy
2024-03-19 15:47 ` Will Deacon
2024-03-19 17:50 ` Jason Gunthorpe
2024-03-22 15:55 ` Will Deacon [this message]
2024-03-22 19:52 ` Tyler Hicks
2024-03-19 18:17 ` Robin Murphy
2024-03-22 15:51 ` Will Deacon
2024-04-02 16:32 ` Robin Murphy
2024-03-19 19:14 ` Tyler Hicks
2024-03-22 16:06 ` Will Deacon
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