From: "Burakov, Anatoly" <anatoly.burakov@intel.com>
To: Takeshi Yoshimura <t.yoshimura8869@gmail.com>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v3] vfio: fix workaround of BAR0 mapping
Date: Fri, 13 Jul 2018 12:08:46 +0100 [thread overview]
Message-ID: <fa6ca8c8-8614-ab5b-ca87-e3e1f1e37248@intel.com> (raw)
In-Reply-To: <4c46da4e-ab67-bb76-b42a-25646c79cd99@intel.com>
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.yoshimura8869@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
next prev parent reply other threads:[~2018-07-13 11:08 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-12 2:44 [dpdk-dev] [PATCH] " Takeshi Yoshimura
2018-07-12 3:08 ` [dpdk-dev] [PATCH v2] " Takeshi Yoshimura
2018-07-12 9:10 ` Burakov, Anatoly
2018-07-13 10:11 ` [dpdk-dev] [PATCH v3] " Takeshi Yoshimura
2018-07-13 11:00 ` Burakov, Anatoly
2018-07-13 11:08 ` Burakov, Anatoly [this message]
2018-07-17 8:21 ` Takeshi Yoshimura
2018-07-17 8:22 ` [dpdk-dev] [PATCH v4] " Takeshi Yoshimura
2018-07-17 10:08 ` Burakov, Anatoly
2018-07-20 8:13 ` [dpdk-dev] [PATCH v5] vfio: fix workaround of BAR mapping Takeshi Yoshimura
2018-07-26 9:35 ` Thomas Monjalon
2018-07-29 8:44 ` Jerin Jacob
2018-07-30 8:51 ` Burakov, Anatoly
2018-07-30 10:03 ` Burakov, Anatoly
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