On Thu, 30 Mar 2017 13:50:27 +0000
Christopher Thompson <chris.thomps...@synopsys.com> wrote:
> Hi,
>
> I'm currently using VFIO for PCI passthrough in a custom simulation, and have
> discovered that when I try to map IO virtual addresses larger than my host
> supports, VFIO happily returns 0 from the dma map ioctl, but dmesg is telling
> me something is wrong.
>
> I noticed this after a few days of wondering why this specific simulation
> wasn't working - the simulated system is trying to setup dma addresses using
> 40-bits of address space, starting at 0xfffffff000 and descending, it turns
> out my host only support 39 bits.
>
> For example a dma map of 0xffffffd000, size 0x1000, the ioctl returns 0 (but
> if I inspect errno it has the value "Bad address"). Dmesg generates the error:
> [677414.285778] intel_iommu_map: iommu width (39) is not sufficient for the
> mapped address (ffffffe000)
>
> I can accept that I can't map addresses larger than my host IOMMU supports,
> but shouldn't VFIO report an error from the mapping?
>
> If this has been fixed in a later version please let me know, my Google-fu
> wasn't good enough to find much on this error. My kernel is a relatively
> ancient 3.13 (Ubuntu 14.04.4).
The kernel version may indeed be the issue, I just modified one of my
test programs to probe the address width using this function:
int probe_iova_limit(int fd, unsigned long vaddr, unsigned long pagesize)
{
struct vfio_iommu_type1_dma_map dma_map = {
.argsz = sizeof(dma_map),
.flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE,
.size = pagesize,
.vaddr = vaddr,
};
struct vfio_iommu_type1_dma_unmap dma_unmap = {
.argsz = sizeof(dma_unmap),
.size = pagesize,
};
int ret;
unsigned long iova = pagesize;
while (iova) {
dma_map.iova = dma_unmap.iova = iova - pagesize;
ret = ioctl(fd, VFIO_IOMMU_MAP_DMA, &dma_map);
if (ret) {
printf("IOMMU failed at 0x%lx (%m), address width %d\n",
dma_map.iova, ffsll(iova) - 2);
return 0;
}
ret = ioctl(fd, VFIO_IOMMU_UNMAP_DMA, &dma_unmap);
if (ret) {
printf("Unmap 0x%lx failed\n", dma_unmap.iova);
return ret;
}
iova <<= 1;
}
printf("IOMMU has full 64 bit address width, no failures\n");
return 0;
}
And my BDW Intel NUC reports:
IOMMU failed at 0xfffffff000 (Bad address), address width 39
An X79 box reports:
IOMMU failed at 0x1fffffffff000 (Bad address), address width 48
Tested both a v4.10 kernel and RHEL7 kernel on the NUC, RHEL7 on the
X79. Try a different kernel, let me know what you find. Thanks,
Alex
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