linux-kernel - Re: [PATCH 18 of 38] x86: unify pci iommu setup and allow swiotlb to compile for 32 bit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1227277292.7186.32.camel@zakaz.uk.xensource.com>
Date:	Fri, 21 Nov 2008 14:21:32 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	jeremy@...p.org, mingo@...e.hu, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com, x86@...nel.org
Subject: Re: [PATCH 18 of 38] x86: unify pci iommu setup and allow swiotlb
	to	compile for 32 bit

On Wed, 2008-11-19 at 11:19 +0900, FUJITA Tomonori wrote:
> 
> The problem that I talked about in the previous mail:
> 
> >       max_slots = mask + 1
> >                   ? ALIGN(mask + 1, 1 << IO_TLB_SHIFT) >> IO_TLB_SHIFT
> >                   : 1UL << (BITS_PER_LONG - IO_TLB_SHIFT);
> 
> Since the popular value of the mask is 0xffffffff. So the above code
> (mask + 1 ?) works wrongly if the size of mask is 32bit (well,
> accidentally the result of max_slots is identical though).

I've just been looking at this again and I don't think it is an accident
that this evaluates to the correct value when mask + 1 == 0.

The patch which adds the "mask + 1 ? ... : 1UL << ..." stuff is:

        commit b15a3891c916f32a29832886a053a48be2741d4d
        Author: Jan Beulich <jbeulich@...ell.com>
        Date:   Thu Mar 13 09:13:30 2008 +0000
        
            avoid endless loops in lib/swiotlb.c
            
            Commit 681cc5cd3efbeafca6386114070e0bfb5012e249 ("iommu sg merging:
            swiotlb: respect the segment boundary limits") introduced two
            possibilities for entering an endless loop in lib/swiotlb.c:
            
             - if max_slots is zero (possible if mask is ~0UL)
             [...]

I think the existing code is the nicest way to handle this corner case
and it is necessary anyway to handle the ~0UL case on 64 bit.

Ian.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/