linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Remove unnecessary WARN_ON

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Date:   Sat, 18 Jan 2020 10:14:11 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, ashok.raj@...el.com,
        jacob.jun.pan@...el.com, kevin.tian@...el.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Remove unnecessary WARN_ON_ONCE()

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@...teo.de>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.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