tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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gpio: virtio: fix DMA alignment

The res and ires buffers in struct virtio_gpio_line and struct
vgpio_irq_line respectively are used for DMA_FROM_DEVICE via
virtqueue_add_sgs(). However, within these structs, even though these
elements are tagged as ____cacheline_aligned, adjacent struct elements
can share DMA cachelines on platforms where ARCH_DMA_MINALIGN >
L1_CACHE_BYTES (e.g., arm64 with 128-byte DMA alignment but 64-byte
cache lines).

The existing ____cacheline_aligned annotation aligns to L1_CACHE_BYTES
which is not always sufficient for DMA alignment. For example, with
L1_CACHE_BYTES = 32 and ARCH_DMA_MINALIGN = 128
- irq_lines[0].ires at offset 128
- irq_lines[1].type at offset 192
both in same 128-byte DMA cacheline [128-256)

When the device writes to irq_lines[0].ires and the CPU concurrently
modifies one of irq_lines[1].type/disabled/masked/queued flags,
corruption can occur on non-cache-coherent platforms.

Fix by using __dma_from_device_group_begin()/end() annotations on the
DMA buffers. Drop ____cacheline_aligned - it's not required to isolate
request and response, and keeping them would increase the memory cost.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Message-ID: <ba7e025a6c84aed012421468d83639e5dae982b0.1767601130.git.mst@redhat.com>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Michael S. Tsirkin 29615fe3 f9108dee

+10 -4
+10 -4
drivers/gpio/gpio-virtio.c
··· 10 10 */ 11 11 12 12 #include <linux/completion.h> 13 + #include <linux/dma-mapping.h> 13 14 #include <linux/err.h> 14 15 #include <linux/gpio/driver.h> 15 16 #include <linux/io.h> ··· 25 24 struct virtio_gpio_line { 26 25 struct mutex lock; /* Protects line operation */ 27 26 struct completion completion; 28 - struct virtio_gpio_request req ____cacheline_aligned; 29 - struct virtio_gpio_response res ____cacheline_aligned; 27 + 28 + __dma_from_device_group_begin(); 29 + struct virtio_gpio_request req; 30 + struct virtio_gpio_response res; 31 + __dma_from_device_group_end(); 30 32 unsigned int rxlen; 31 33 }; 32 34 ··· 41 37 bool update_pending; 42 38 bool queue_pending; 43 39 44 - struct virtio_gpio_irq_request ireq ____cacheline_aligned; 45 - struct virtio_gpio_irq_response ires ____cacheline_aligned; 40 + __dma_from_device_group_begin(); 41 + struct virtio_gpio_irq_request ireq; 42 + struct virtio_gpio_irq_response ires; 43 + __dma_from_device_group_end(); 46 44 }; 47 45 48 46 struct virtio_gpio {