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

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

On 16-Nov-18 2:34 AM, Tone Zhang (Arm Technology China) wrote:
> Hi Anatoly,
> 
> I have some comments.
> 
>> -----Original Message-----
>> From: Tone Zhang (Arm Technology China)
>> Sent: Thursday, November 15, 2018 8:49 AM
>> To: Burakov, Anatoly <anatoly.burakov@intel.com>; dev@dpdk.org
>> Cc: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Honnappa
>> Nagarahalli <Honnappa.Nagarahalli@arm.com>; Steve Capper
>> <Steve.Capper@arm.com>; nd <nd@arm.com>
>> Subject: RE: [PATCH v2] pci_vfio: Support 64KB kernel page_size with vfio-pci
>> driver
>>
>> Hi Anatoly,
>>
>> Sorry for the late response.
>>
>>> -----Original Message-----
>>> From: Burakov, Anatoly <anatoly.burakov@intel.com>
>>> Sent: Friday, November 9, 2018 8:15 PM
>>> To: Tone Zhang (Arm Technology China) <Tone.Zhang@arm.com>;
>>> dev@dpdk.org
>>> Cc: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Honnappa
>>> Nagarahalli <Honnappa.Nagarahalli@arm.com>; Steve Capper
>>> <Steve.Capper@arm.com>; nd <nd@arm.com>
>>> Subject: Re: [PATCH v2] pci_vfio: Support 64KB kernel page_size with
>>> vfio-pci driver
>>>
>>> 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 :)
>>
>> Thanks a lot! Will keep in mind. 😊
>>
>>>
>>>> ---
>>>>    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.
>>>
>>
>> Will update the code in next version. Thanks!
>>
>>>> +		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.
>>>
>>
>> Will update the patch.
>>
> 
> When enter the judgement, it implies the "msix_table->offset" is NOT page size aligned, I think we can replace the code in the judgement with one line: table_start = msix_table->offset;
> It looks more simple. What's your opinion? Thanks!

Agree, what was i thinking :D

> 
>>>> +			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.
>>>
>>
>> Thanks a lot. Will update.
>>
>>>> +			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! 😉
>>
>>> --
>>> Thanks,
>>> Anatoly
>>
>> Br,
>> Tone
> 
> Br,
> Tone
> 


-- 
Thanks,
Anatoly