Re: [dpdk-dev] [PATCH v2] pci_vfio: Support 64KB kernel page_size with vfio-pci driver

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 09-Nov-18 5:57 AM, tone.zhang wrote:
> With a larger PAGE_SIZE it is possible for the MSI table to very
> close to the end of the BAR s.t. when we align the start and end
> of the MSI table to the PAGE_SIZE, the end offset of the MSI
> table is out of the PCI BAR boundary.
> 
> This patch addresses the issue by comparing both the start and the
> end offset of the MSI table with the BAR size, and skip the mapping
> if it is out of Bar scope.
> 
> The patch fixes the debug log as below:
> EAL: Skipping BAR0
> 
> Signed-off-by: tone.zhang <tone.zhang@arm.com>
> Reviewed-by: Gavin Hu <Gavin.Hu@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Steve Capper <Steve.Capper@arm.com>
> Reviewed-by: Burakov Anatoly <anatoly.burakov@intel.com>

In the future, please don't include my Reviewed tag unless i actually 
sent one :)

> ---
>   drivers/bus/pci/linux/pci_vfio.c | 36 +++++++++++++++++++++++++++++++-----
>   1 file changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/bus/pci/linux/pci_vfio.c b/drivers/bus/pci/linux/pci_vfio.c
> index 305cc06..9a0affe 100644
> --- a/drivers/bus/pci/linux/pci_vfio.c
> +++ b/drivers/bus/pci/linux/pci_vfio.c
> @@ -445,9 +445,11 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct mapped_pci_resource *vfio_res,
>   	struct pci_msix_table *msix_table = &vfio_res->msix_table;
>   	struct pci_map *bar = &vfio_res->maps[bar_index];
>   
> -	if (bar->size == 0)
> +	if (bar->size == 0) {
>   		/* Skip this BAR */
> +		RTE_LOG(INFO, EAL, "Skipping BAR%d\n", bar_index);
>   		return 0;
> +	}
>   
>   	if (msix_table->bar_index == bar_index) {
>   		/*
> @@ -456,8 +458,22 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct mapped_pci_resource *vfio_res,
>   		 */
>   		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;
> +		table_end = RTE_ALIGN(table_end, PAGE_SIZE);
> +		table_start = RTE_ALIGN(table_start, PAGE_SIZE);
> +		/* after rounding to PAGE_SIZE, it is over the bar->size,
> +		 * fall back to the MSI-X table offset in the bar and
> +		 * align with PAGE_SIZE.
> +		 */

Minor nitpick - wording of comment could be better, for example:

if page-aligned start of MSI-X table is beyond BAR size, shrink the 
mapping size to MSI-X table start address.

Also, probably needs newline before comment.

> +		if (table_start >= bar->size) {
> +			table_start = RTE_ALIGN_FLOOR(msix_table->offset,
> +							PAGE_SIZE);
> +			/* after aligning with PAGE_SIZE, if it is less than
> +			 * the MSI-X table offset, continue falling back to
> +			 * the actual MSI-X table offset in the bar.
> +			 */

Same here, wording could probably be improved. Suggested rewording:

If MSI-X table address, floor-aligned by page size, is lower than actual 
MSI-X table offset, fall back to using MSI-X table offset as table start.

Now that i think of it, this could really be expressed like this:

uint32_t aligned = RTE_ALIGN_FLOOR(msix_table->offset, PAGE_SIZE);
table_start = RTE_MAX(aligned, msix_table_offset);

I believe this would be much clearer.

> +			if (table_start < msix_table->offset)
> +				table_start = msix_table->offset;
> +		}
>   
>   		if (table_start == 0 && table_end >= bar->size) {
>   			/* Cannot map this BAR */
> @@ -469,8 +485,18 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct mapped_pci_resource *vfio_res,
>   
>   		memreg[0].offset = bar->offset;
>   		memreg[0].size = table_start;
> -		memreg[1].offset = bar->offset + table_end;
> -		memreg[1].size = bar->size - table_end;
> +		if (bar->size < table_end) {
> +			/*
> +			 * after rounding to PAGE_SIZE we don't have any space
> +			 * left after the MSI table, so don't try and map it.
> +			 */

Suggested rewording:

If MSI-X table end is beyond BAR end, don't attempt to perform second 
mapping.

> +			memreg[1].offset = 0;
> +			memreg[1].size = 0;
> +		}
> +		else {
> +			memreg[1].offset = bar->offset + table_end;
> +			memreg[1].size = bar->size - table_end;
> +		}
>   
>   		RTE_LOG(DEBUG, EAL,
>   			"Trying to map BAR%d that contains the MSI-X "
> 

However, the patch can go in as is if needed, so

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

-- 
Thanks,
Anatoly