On Wed, Jul 31, 2019 at 11:40 PM Gerd Hoffmann kraxel@redhat.com wrote:
On Wed, Jul 31, 2019 at 07:25:13PM -0700, Gurchetan Singh wrote:
The main use for udmabuf is sending guest memory pages to the host.
It's generally a bad idea to have to separate mappings with different attributes. For example, a WC mapping the guest kernel and cached mapping on the host is problematic.
Add creation time flags so the user has responsibility for the specific use case.
-#define UDMABUF_FLAGS_CLOEXEC 0x01 +#define UDMABUF_FLAGS_CLOEXEC 0x01 +#define UDMABUF_FLAGS_PROT_NONE 0x02 +#define UDMABUF_FLAGS_PROT_READ 0x04 +#define UDMABUF_FLAGS_PROT_WRITE 0x08
[ didn't look at followup patches yet ]
You can't have readonly/writeonly dmabufs. So that isn't going to fly.
The commit message suggests this is for cache attributes not protection, so having the flags might make sense, but please don't name the flags PROT_* then.
Okay, I'll change the flags to CACHED / UNCACHED / WRITE_COMBINE (like msm_drm.h). And since the dma api doesn't work on x86 [1], we'll have to call drm_cflush_pages in the guest. Since caching is privileged on ARM and not on x86, that *should* get us write-combine guest buffers.
[1] https://lists.freedesktop.org/archives/dri-devel/2019-August/229161.html
cheers, Gerd