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Message-ID: <20250902092920.GE10073@unreal>
Date: Tue, 2 Sep 2025 12:29:20 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>,
Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Abdiel Janulgue <abdiel.janulgue@...il.com>,
Alexander Potapenko <glider@...gle.com>,
Alex Gaynor <alex.gaynor@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Hellwig <hch@....de>, Danilo Krummrich <dakr@...nel.org>,
iommu@...ts.linux.dev, Jason Wang <jasowang@...hat.com>,
Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
Jonathan Corbet <corbet@....net>, Juergen Gross <jgross@...e.com>,
kasan-dev@...glegroups.com, Keith Busch <kbusch@...nel.org>,
linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-nvme@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
linux-trace-kernel@...r.kernel.org,
Madhavan Srinivasan <maddy@...ux.ibm.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
"Michael S. Tsirkin" <mst@...hat.com>,
Miguel Ojeda <ojeda@...nel.org>,
Robin Murphy <robin.murphy@....com>, rust-for-linux@...r.kernel.org,
Sagi Grimberg <sagi@...mberg.me>,
Stefano Stabellini <sstabellini@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>,
xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v4 00/16] dma-mapping: migrate to physical address-based
API
On Mon, Sep 01, 2025 at 07:23:02PM -0300, Jason Gunthorpe wrote:
> On Mon, Sep 01, 2025 at 11:47:59PM +0200, Marek Szyprowski wrote:
> > I would like to give those patches a try in linux-next, but in meantime
> > I tested it on my test farm and found a regression in dma_map_resource()
> > handling. Namely the dma_map_resource() is no longer possible with size
> > not aligned to kmalloc()'ed buffer, as dma_direct_map_phys() calls
> > dma_kmalloc_needs_bounce(),
>
> Hmm, it's this bit:
>
> capable = dma_capable(dev, dma_addr, size, !(attrs & DMA_ATTR_MMIO));
> if (unlikely(!capable) || dma_kmalloc_needs_bounce(dev, size, dir)) {
> if (is_swiotlb_active(dev) && !(attrs & DMA_ATTR_MMIO))
> return swiotlb_map(dev, phys, size, dir, attrs);
>
> goto err_overflow;
> }
>
> We shouldn't be checking dma_kmalloc_needs_bounce() on mmio as there
> is no cache flushing so the "dma safe alignment" for non-coherent DMA
> does not apply.
>
> Like you say looks good to me, and more of the surrouding code can be
> pulled in too, no sense in repeating the boolean logic:
>
> if (attrs & DMA_ATTR_MMIO) {
> dma_addr = phys;
> if (unlikely(!dma_capable(dev, dma_addr, size, false)))
> goto err_overflow;
> } else {
> dma_addr = phys_to_dma(dev, phys);
> if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
I tried to reuse same code as much as possible :(
> dma_kmalloc_needs_bounce(dev, size, dir)) {
> if (is_swiotlb_active(dev))
> return swiotlb_map(dev, phys, size, dir, attrs);
>
> goto err_overflow;
> }
> if (!dev_is_dma_coherent(dev) &&
> !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> arch_sync_dma_for_device(phys, size, dir);
> }
Like Jason wrote, but in diff format:
diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
index 92dbadcd3b2f..3f4792910604 100644
--- a/kernel/dma/direct.h
+++ b/kernel/dma/direct.h
@@ -85,7 +85,6 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
unsigned long attrs)
{
dma_addr_t dma_addr;
- bool capable;
if (is_swiotlb_force_bounce(dev)) {
if (attrs & DMA_ATTR_MMIO)
@@ -94,17 +93,19 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,
return swiotlb_map(dev, phys, size, dir, attrs);
}
- if (attrs & DMA_ATTR_MMIO)
+ if (attrs & DMA_ATTR_MMIO) {
dma_addr = phys;
- else
+ if (unlikely(dma_capable(dev, dma_addr, size, false)))
+ goto err_overflow;
+ } else {
dma_addr = phys_to_dma(dev, phys);
+ if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
+ dma_kmalloc_needs_bounce(dev, size, dir)) {
+ if (is_swiotlb_active(dev))
+ return swiotlb_map(dev, phys, size, dir, attrs);
- capable = dma_capable(dev, dma_addr, size, !(attrs & DMA_ATTR_MMIO));
- if (unlikely(!capable) || dma_kmalloc_needs_bounce(dev, size, dir)) {
- if (is_swiotlb_active(dev) && !(attrs & DMA_ATTR_MMIO))
- return swiotlb_map(dev, phys, size, dir, attrs);
-
- goto err_overflow;
+ goto err_overflow;
+ }
}
if (!dev_is_dma_coherent(dev) &&
I created new tag with fixed code.
https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/tag/?h=dma-phys-Sep-2
Thanks
>
> Jason
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