From: Walter Wu <walter-zh.wu@mediatek.com>
To: Ard Biesheuvel <ardb@kernel.org>, Christoph Hellwig <hch@lst.de>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
wsd_upstream <wsd_upstream@mediatek.com>,
<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v2] dma-direct: improve DMA_ATTR_NO_KERNEL_MAPPING
Date: Thu, 4 Nov 2021 20:31:00 +0800 [thread overview]
Message-ID: <cc893162f0e2c81a1d64bf85794cc77ae76cadce.camel@mediatek.com> (raw)
In-Reply-To: <CAMj1kXHjjmhCVzKFhAseMGOdnidmFT=+o+vwKLTCGFkpwHmcfQ@mail.gmail.com>
On Thu, 2021-11-04 at 09:57 +0100, Ard Biesheuvel wrote:
> On Thu, 4 Nov 2021 at 09:53, Christoph Hellwig <hch@lst.de> wrote:
> >
> > On Thu, Nov 04, 2021 at 10:32:21AM +0800, Walter Wu wrote:
> > > diff --git a/include/linux/set_memory.h
> > > b/include/linux/set_memory.h
> > > index f36be5166c19..6c7d1683339c 100644
> > > --- a/include/linux/set_memory.h
> > > +++ b/include/linux/set_memory.h
> > > @@ -7,11 +7,16 @@
> > >
> > > #ifdef CONFIG_ARCH_HAS_SET_MEMORY
> > > #include <asm/set_memory.h>
> > > +
> > > +#ifndef CONFIG_RODATA_FULL_DEFAULT_ENABLED
> >
> > This is an arm64-specific symbol, and one that only controls a
> > default. I don't think it is suitable to key off stubs in common
> > code.
> >
> > > +static inline int set_memory_valid(unsigned long addr, int
> > > numpages, int enable) { return 0; }
> >
> > Pleae avoid overly long lines.
> >
> > > + if (IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED))
> > > {
> > > + kaddr = (unsigned
> > > long)phys_to_virt(dma_to_phys(dev, *dma_handle));
> >
> > This can just use page_address.
> >
> > > + /* page remove kernel mapping for arm64 */
> > > + set_memory_valid(kaddr, size >> PAGE_SHIFT,
> > > 0);
> > > + }
> >
> > But more importantly: set_memory_valid only exists on arm64, this
> > will break compile everywhere else. And this API is complete crap.
> > Passing kernel virtual addresses as unsigned long just sucks, and
> > passing an integer argument for valid/non-valid also is a horrible
> > API.
> >
>
> ... and as I pointed out before, you can still pass rodata=off on
> arm64, and get the old behavior, in which case bad things will happen
> if you try to use an API that expects to operate on page mappings
> with
> a 1 GB block mapping.
>
Thanks for your suggestion.
> And you still haven't explained what the actual problem is: is this
> about CPU speculation corrupting non-cache coherent inbound DMA?
No corrupiton, only cpu read it, we hope to fix the behavior.
Thanks.
Walter
next prev parent reply other threads:[~2021-11-04 12:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-04 2:32 [PATCH v2] dma-direct: improve DMA_ATTR_NO_KERNEL_MAPPING Walter Wu
2021-11-04 8:53 ` Christoph Hellwig
2021-11-04 8:57 ` Ard Biesheuvel
2021-11-04 12:31 ` Walter Wu [this message]
2021-11-04 12:47 ` Ard Biesheuvel
2021-11-04 13:40 ` Walter Wu
2021-11-04 16:22 ` Ard Biesheuvel
2021-11-04 12:18 ` Walter Wu
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