Re: [PATCH 0/2] riscv: implement Zicbom-based CMO instructions + the t-head variant

Corentin Labbe
2022-04-16T07:35:42Z

Le Fri, Apr 15, 2022 at 09:19:23PM -0500, Samuel Holland a écrit :
> On 4/15/22 6:26 AM, Corentin Labbe wrote:
> > Le Mon, Mar 07, 2022 at 11:46:18PM +0100, Heiko Stuebner a écrit :
> >> This series is based on the alternatives changes done in my svpbmt series
> >> and thus also depends on Atish's isa-extension parsing series.
> >>
> >> It implements using the cache-management instructions from the Zicbom-
> >> extension to handle cache flush, etc actions on platforms needing them.
> >>
> >> SoCs using cpu cores from T-Head like the Allwinne D1 implement a
> >> different set of cache instructions. But while they are different,
> >> instructions they provide the same functionality, so a variant can
> >> easly hook into the existing alternatives mechanism on those.
> >>
> >>
> >
> > Hello
> >
> > I am testing https://github.com/smaeul/linux.git branch:origin/riscv/d1-wip which contain this serie.
> >
> > I am hitting a buffer corruption problem with DMA.
> > The sun8i-ce crypto driver fail self tests due to "device overran destination buffer".
> > In fact the buffer is not overran by device but by dma_map_single() operation.
> >
> > The following small code show the problem:
> >
> > dma_addr_t dma;
> > u8 *buf;
> > #define BSIZE 2048
> > #define DMASIZE 16
> >
> > buf = kmalloc(BSIZE, GFP_KERNEL | GFP_DMA);
> > for (i = 0; i < BSIZE; i++)
> > buf[i] = 0xFE;
> > print_hex_dump(KERN_INFO, "DMATEST1:", DUMP_PREFIX_NONE, 16, 4, buf, 256, false);
> > dma = dma_map_single(ce->dev, buf, DMASIZE, DMA_FROM_DEVICE);
>
> This function (through dma_direct_map_page()) ends up calling
> arch_sync_dma_for_device(..., ..., DMA_FROM_DEVICE), which invalidates the CPU's
> cache. This is the same thing other architectures do (at least arm, arm64,
> openrisc, and powerpc). So this appears to be working as intended.
>
> Regards,
> Samuel
>

This behavour is not present at least on ARM and ARM64.
The sample code I provided does not corrupt the buffer on them.

Regards