On 13-Jul-18 12:00 PM, Burakov, Anatoly wrote:
On 13-Jul-18 11:11 AM, Takeshi Yoshimura wrote:
The workaround of BAR0 mapping gives up and immediately returns an
error if it cannot map around the MSI-X. However, recent version
of VFIO allows MSIX mapping (*).
I fixed not to return immediately but try mapping. In old Linux, mmap
just fails and returns the same error as the code before my fix . In
recent Linux, mmap succeeds and this patch enables running DPDK in
specific environments (e.g., ppc64le with HGST NVMe)
(*): "vfio-pci: Allow mapping MSIX BAR",
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
commit/id=a32295c612c57990d17fb0f41e7134394b2f35f6
Fixes: 90a1633b2347 ("eal/linux: allow to map BARs with MSI-X tables")
Signed-off-by: Takeshi Yoshimura <t.yoshimura8...@gmail.com>
---
Thanks, Anatoly.
I updated the patch not to affect behaviors of older Linux and
other environments as well as possible. This patch adds another
chance to mmap BAR0.
I noticed that the check at line 350 already includes the check
of page size, so this patch does not fix the check.
Regards,
Takeshi
Hi Takeshi,
Please correct me if i'm wrong, but i'm not sure the old behavior is kept.
Let's say we're running an old kernel, which doesn't allow mapping MSI-X
BARs. If MSI-X starts at beginning of the BAR (floor-aligned to page
size), and ends at or beyond end of BAR (ceiling-aligned to page size).
In that situation, old code just skipped the BAR and returned 0.
We then exited the function, and there's a check for return value right
after pci_vfio_mmap_bar() that stop continuing if we fail to map
something. In the old code, we would continue as we went, and finish the
rest of our mappings. With your new code, you're attempting to map the
BAR, it fails, and you will return -1 on older kernels.
I believe what we really need here is the following:
1) If this is a BAR containing MSI-X vector, first try mapping the
entire BAR. If it succeeds, great - that would be your new kernel behavior.
2) If we failed on step 1), check to see if we can map around the BAR.
If we can, try to map around it like the current code does. If we cannot
map around it (i.e. if MSI-X vector, page aligned, occupies entire BAR),
then we simply return 0 and skip the BAR.
That, i would think, would keep the old behavior and enable the new one.
Does that make sense?
I envision this to look something like this:
bool again = false;
do {
if (again) {
// set up mmap-around
if (cannot map around)
return 0;
}
// try mapping
if (map_failed && msix_table->bar_index == bar_index) {
again = true;
continue;
}
if (map_failed)
return -1;
break/return 0;
} while (again);
--
Thanks,
Anatoly
