Re: [PATCH 1/1] iommu/vt-d: Remove unnecessary WARN_ON_ONCE()

Lu Baolu
2020-01-18T02:15:41Z

Hi Joerg,

On 1/17/20 5:59 PM, Joerg Roedel wrote:
> On Thu, Jan 16, 2020 at 09:52:36AM +0800, Lu Baolu wrote:
>> Address field in device TLB invalidation descriptor is qualified
>> by the S field. If S field is zero, a single page at page address
>> specified by address [63:12] is requested to be invalidated. If S
>> field is set, the least significant bit in the address field with
>> value 0b (say bit N) indicates the invalidation address range. The
>> spec doesn't require the address [N - 1, 0] to be cleared, hence
>> remove the unnecessary WARN_ON_ONCE().
>>
>> Otherwise, the caller might set "mask = MAX_AGAW_PFN_WIDTH" in order
>> to invalidating all the cached mappings on an endpoint, and below
>> overflow error will be triggered.
>>
>> [...]
>> UBSAN: Undefined behaviour in drivers/iommu/dmar.c:1354:3
>> shift exponent 64 is too large for 64-bit type 'long long unsigned int'
>> [...]
>>
>> Reported-and-tested-by: Frank <fgndev@posteo.de>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>
> Does this need a Fixes and/or stable tag?
>

This doesn't cause any errors, just an unnecessary checking of

"0 & ((1UL << 64) - 1)"

in some cases.

>
> Regards,
>
> Joerg

Best regards,
baolu