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

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Message-ID: <20200124143648.GC27081@8bytes.org>
Date:   Fri, 24 Jan 2020 15:36:48 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     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()

On Sat, Jan 18, 2020 at 10:14:11AM +0800, Lu Baolu wrote:
> 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.

Okay, applied for v5.6.