From: Dave Young <dyoung@redhat.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Kairui Song <kasong@redhat.com>,
anthony.yznaga@oracle.com,
Jan Setje-Eilers <jan.setjeeilers@oracle.com>,
Alexander Graf <graf@amazon.com>,
iommu@lists.linux-foundation.org,
the arch/x86 maintainers <x86@kernel.org>,
Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
linux-doc@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
dwmw@amazon.com, benh@amazon.com,
Jan Kiszka <jan.kiszka@siemens.com>,
alcioa@amazon.com, aggh@amazon.com, aagch@amazon.com,
dhr@amazon.com, Laszlo Ersek <lersek@redhat.com>,
Baoquan He <bhe@redhat.com>, Lianbo Jiang <lijiang@redhat.com>,
brijesh.singh@amd.com, "Lendacky,
Thomas" <thomas.lendacky@amd.com>,
kexec@lists.infradead.org
Subject: Re: [PATCH] swiotlb: Allow swiotlb to live at pre-defined address
Date: Tue, 31 Mar 2020 09:46:32 +0800 [thread overview]
Message-ID: <20200331014632.GA81569@dhcp-128-65.nay.redhat.com> (raw)
In-Reply-To: <20200330134004.GA31026@char.us.oracle.com>
On 03/30/20 at 09:40am, Konrad Rzeszutek Wilk wrote:
> On Mon, Mar 30, 2020 at 02:06:01PM +0800, Kairui Song wrote:
> > On Sat, Mar 28, 2020 at 7:57 PM Dave Young <dyoung@redhat.com> wrote:
> > >
> > > On 03/26/20 at 05:29pm, Alexander Graf wrote:
> > > > The swiotlb is a very convenient fallback mechanism for bounce buffering of
> > > > DMAable data. It is usually used for the compatibility case where devices
> > > > can only DMA to a "low region".
> > > >
> > > > However, in some scenarios this "low region" may be bound even more
> > > > heavily. For example, there are embedded system where only an SRAM region
> > > > is shared between device and CPU. There are also heterogeneous computing
> > > > scenarios where only a subset of RAM is cache coherent between the
> > > > components of the system. There are partitioning hypervisors, where
> > > > a "control VM" that implements device emulation has limited view into a
> > > > partition's memory for DMA capabilities due to safety concerns.
> > > >
> > > > This patch adds a command line driven mechanism to move all DMA memory into
> > > > a predefined shared memory region which may or may not be part of the
> > > > physical address layout of the Operating System.
> > > >
> > > > Ideally, the typical path to set this configuration would be through Device
> > > > Tree or ACPI, but neither of the two mechanisms is standardized yet. Also,
> > > > in the x86 MicroVM use case, we have neither ACPI nor Device Tree, but
> > > > instead configure the system purely through kernel command line options.
> > > >
> > > > I'm sure other people will find the functionality useful going forward
> > > > though and extend it to be triggered by DT/ACPI in the future.
> > >
> > > Hmm, we have a use case for kdump, this maybe useful. For example
> > > swiotlb is enabled by default if AMD SME/SEV is active, and in kdump
> > > kernel we have to increase the crashkernel reserved size for the extra
> > > swiotlb requirement. I wonder if we can just reuse the old kernel's
> > > swiotlb region and pass the addr to kdump kernel.
> > >
> >
> > Yes, definitely helpful for kdump kernel. This can help reduce the
> > crashkernel value.
> >
> > Previously I was thinking about something similar, play around the
> > e820 entry passed to kdump and let it place swiotlb in wanted region.
> > Simply remap it like in this patch looks much cleaner.
> >
> > If this patch is acceptable, one more patch is needed to expose the
> > swiotlb in iomem, so kexec-tools can pass the right kernel cmdline to
> > second kernel.
>
> We seem to be passsing a lot of data to kexec.. Perhaps something
> of a unified way since we seem to have a lot of things to pass - disabling
> IOMMU, ACPI RSDT address, and then this.
acpi_rsdp kernel cmdline is not useful anymore. The initial purpose is
for kexec-rebooting in efi system. But now we have supported efi boot
across kexec reboot thus that is useless now.
Thanks
Dave
prev parent reply other threads:[~2020-03-31 1:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-26 16:29 [PATCH] swiotlb: Allow swiotlb to live at pre-defined address Alexander Graf
2020-03-26 17:05 ` Christoph Hellwig
2020-03-26 17:11 ` Alexander Graf
2020-03-26 17:16 ` David Woodhouse
2020-03-30 13:24 ` Mark Rutland
2020-03-27 6:05 ` kbuild test robot
2020-03-27 9:58 ` Jan Kiszka
2020-03-28 11:57 ` Dave Young
2020-03-30 6:06 ` Kairui Song
2020-03-30 13:40 ` Konrad Rzeszutek Wilk
2020-03-30 20:42 ` Alexander Graf
2020-03-30 23:37 ` Anthony Yznaga
2020-03-31 1:59 ` Dave Young
2020-03-31 2:16 ` Baoquan He
2020-03-31 1:46 ` Dave Young [this message]
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