From: Christoph Hellwig <hch@infradead•org>
To: Stefano Stabellini <sstabellini@kernel•org>
Cc: jgross@suse•com, Peng Fan <peng.fan@nxp•com>,
Catalin Marinas <Catalin.Marinas@arm•com>,
"linux@armlinux•org.uk" <linux@armlinux•org.uk>,
Christoph Hellwig <hch@infradead•org>,
Julien Grall <Julien.Grall@arm•com>,
dl-linux-imx <linux-imx@nxp•com>,
"xen-devel@lists•xenproject.org" <xen-devel@lists•xenproject.org>,
boris.ostrovsky@oracle•com, nd <nd@arm•com>,
"will@kernel•org" <will@kernel•org>,
"linux-arm-kernel@lists•infradead.org"
<linux-arm-kernel@lists•infradead.org>,
Robin Murphy <Robin.Murphy@arm•com>
Subject: Re: [PATCH V2] arm: xen: mm: use __GPF_DMA32 for arm64
Date: Mon, 2 Sep 2019 08:57:32 -0700 [thread overview]
Message-ID: <20190902155732.GA8311@infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.21.1908301926500.21347@sstabellini-ThinkPad-T480s>
On Fri, Aug 30, 2019 at 07:40:42PM -0700, Stefano Stabellini wrote:
> + Juergen, Boris
>
> On Fri, 30 Aug 2019, Christoph Hellwig wrote:
> > Can we take a step back and figure out what we want to do here?
> >
> > AFAICS this function allocates memory for the swiotlb-xen buffer,
> > and that means it must be <= 32-bit addressable to satisfy the DMA API
> > guarantees. That means we generally want to use GFP_DMA32 everywhere
> > that exists, but on systems with odd zones we might want to dip into
> > GFP_DMA. This also means swiotlb-xen doesn't actually do the right
> > thing on x86 at the moment. So shouldn't we just have one common
> > routine in swiotlb-xen.c that checks if we have CONFIG_ZONE_DMA32
> > set, then try GFP_DMA32, and if not check if CONFIG_ZONE_DMA is set
> > and then try that, else default to GFP_KERNEL?
>
> Yes, for ARM/ARM64 it makes a lot of sense given that dom0 is 1:1 mapped
> (pseudo-physical == physical). I'll let Juergen and Boris comment on
> the x86 side of things, but on x86 PV Dom0 is not 1:1 mapped so
> GFP_DMA32 is probably not meaningful.
But is it actually harmful? If the GFP_DMA32 doesn't hurt we could
just use it there. Or if that seems to ugly we can make the dma
flags dependents on a XEN_1TO1_MAPPED config option set by arm/arm64.
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next prev parent reply other threads:[~2019-09-02 15:57 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 2:28 [PATCH V2] arm: xen: mm: use __GPF_DMA32 for arm64 Peng Fan
2019-08-30 8:39 ` Julien Grall
2019-08-30 8:58 ` Christoph Hellwig
2019-08-31 2:40 ` Stefano Stabellini
2019-09-02 15:57 ` Christoph Hellwig [this message]
2019-09-03 11:48 ` Juergen Gross
2019-09-11 2:06 ` Peng Fan
2019-09-11 19:12 ` Stefano Stabellini
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