linux-kernel - Re: [PATCH v7u1 26/31] x86: Don't enable swiotlb if there is not enough ram for it

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Date:	Fri, 4 Jan 2013 19:02:06 -0700
From:	Shuah Khan <shuahkhan@...il.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Jan Kiszka <jan.kiszka@....de>,
	Jason Wessel <jason.wessel@...driver.com>,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v7u1 26/31] x86: Don't enable swiotlb if there is not
 enough ram for it

On Fri, Jan 4, 2013 at 4:55 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Fri, Jan 4, 2013 at 3:21 PM, Shuah Khan <shuahkhan@...il.com> wrote:
>
>> Please see attached dmesg for full log. I can do some testing on this
>> system with your patch if you would like.
>
> That would be great.
>
> Please try
> git://git.kernel.org/pub/scm/linux/kernel/git/yinghai/linux-yinghai.git
> for-x86-boot
> or just this patch.
>
> Too bad, I can not access AMD systems with IOMMU support.
>
> Thanks a lot.

I tried your patch on my AMD system. I did change the patch to print
warning instead of panic() and it did trigger the condition for
panic.:

[    5.376654] AMD-Vi: Found IOMMU at 0000:00:00.2 cap 0x40
[    5.376717]
[    5.376799] pci 0000:00:00.2: irq 72 for MSI/MSI-X

It would have panic'ed here:

[    5.388858] AMD-Vi: can not enable swiotlb for unhandled devices by
AMD iommu!

[    5.388964] AMD-Vi: Lazy IO/TLB flushing enabled
[    5.389324] LVT offset 0 assigned for vector 0x400

I applied your patch to 3.6.11 and changed the panic() to pr_info()
and also changed enough_mem_for_swiotlb() to always return false to
simulate not enough memory condition as this system does have enough
memory.

So at least on this AMD system, your patch will result in a panic.

Thanks,
-- Shuah
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