[dpdk-dev] [PATCH v4] vfio: fix workaround of BAR0 mapping

[Burakov, Anatoly]

On 17-Jul-18 9:22 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)

I don't think this applies to BAR0 only - it can be any BAR. Suggested 
rewording:

Currently, VFIO will try to map around MSI-X table in the BARs. When 
MSI-X table (page-aligned) size is equal to (page-aligned) size of BAR, 
VFIO will just skip the BAR.

Recent kernel versions will allow VFIO to map the entire BAR containing 
MSI-X tables (*), so instead of trying to map around the MSI-X vector or 
skipping the BAR entirely if it's not possible, we can now try mapping 
the entire BAR first. If mapping the entire BAR doesn't succeed, fall 
back to the old behavior of mapping around MSI-X table or skipping the BAR.

> 
> (*): "vfio-pci: Allow mapping MSIX BAR",
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
> commit/id=a32295c612c57990d17fb0f41e7134394b2f35f6

I think your link is wrong here - at least i can't find the commit when 
i copypaste the link into my browser.

> 
> Fixes: 90a1633b2347 ("eal/linux: allow to map BARs with MSI-X tables")
> 
> Signed-off-by: Takeshi Yoshimura <t.yoshimura8869 at gmail.com>
> ---

<snip>

> +	memreg[0].offset = bar->offset;
> +	memreg[0].size = bar->size;
> +	do {
>   		void *map_addr = NULL;
> +		if (again) {
> +			/*
> +			 * VFIO did not let us map the MSI-X table,
> +			 * but we can map around it.
> +			 */
> +			uint32_t table_start = msix_table->offset;
> +			uint32_t table_end = table_start + msix_table->size;
> +			table_end = (table_end + ~PAGE_MASK) & PAGE_MASK;
> +			table_start &= PAGE_MASK;
> +
> +			if (table_start == 0 && table_end >= bar->size) {
> +				/* Cannot map this BAR */
> +				RTE_LOG(DEBUG, EAL, "Skipping BAR%d\n",
> +						bar_index);
> +				bar->size = 0;
> +				bar->addr = 0;
> +				return 0;

You have reserved space for the BAR earlier but do not unmap it on return.

Once that is fixed,

Reviewed-by: Anatoly Burakov <anatoly.burakov at intel.com>

-- 
Thanks,
Anatoly