linux-kernel - Re: vmalloced stacks on x86

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Message-ID: <CALCETrV6fFKx7F18ox8MkdezDittsmsaSZC4H9rc8LL3-myzgA@mail.gmail.com>
Date:	Sat, 25 Oct 2014 09:05:05 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>
Subject: Re: vmalloced stacks on x86_64?

On Oct 25, 2014 2:15 AM, "Ingo Molnar" <mingo@...nel.org> wrote:
>
>
> * Andy Lutomirski <luto@...capital.net> wrote:
>
> > Is there any good reason not to use vmalloc for x86_64 stacks?
>
> In addition to what hpa mentioned, __pa()/__va() on-kstack DMA
> gets tricky, for legacy drivers. (Not sure how many of these are
> left though.)

Hopefully very few.  DMA debugging warns if the driver uses the DMA
API, and if the driver doesn't, then IOMMUs will break it.

virtio-net is an oddball offender.  I have a patch.

--Andy

>
> Thanks,
>
>         Ingo
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