linux-kernel - Re: [Xen-devel] kasan_map_early

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Date:	Wed, 04 Mar 2015 05:53:04 +0100
From:	Juergen Gross <jgross@...e.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Jan Beulich <JBeulich@...e.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Chris Wright <chrisw@...s-sol.org>,
	xen-devel@...ts.xenproject.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	virtualization@...ts.linux-foundation.org,
	Alok Kataria <akataria@...are.com>
Subject: Re: [Xen-devel] kasan_map_early_shadow() on Xen

On 03/03/2015 08:20 PM, Luis R. Rodriguez wrote:
> On Tue, Mar 3, 2015 at 2:06 AM, David Vrabel <david.vrabel@...rix.com> wrote:
>> On 03/03/15 09:40, Luis R. Rodriguez wrote:
>>> Andrey,
>>>
>>> I believe that on Xen we should disable kasan, would like confirmation
>>
>> Why?  This is the first of heard of this.
>
> Andrey chimed in here confirming this.
>
>>> from someone on xen-devel though. Here's the thing though -- if true
>>> -- I'd like to do it *properly*, where *properly* means addressing a
>>> bit of architecture. A simple Kconfig slap seems rather reactive. I'd
>>> like to address a way to properly ensure we don't run into this and
>>> other similar issues in the future. The CR4 shadow issue was another
>>> recent example issue, also introduced via v4.0 [0]. We can't keep
>>> doing this reactively.
>>>
>>> Let's go down the rabbit hole for a bit. HAVE_ARCH_KASAN will be
>>> selected on x86 when:
>>>
>>> if X86_64 && SPARSEMEM_VMEMMAP
>>>
>>> Now Xen should not have SPARSEMEM_VMEMMAP but PVOPs' goal is to enable
>>
>> Why?  Again, this is the first I've heard of this as well.  FWIW, all
>> the Xen configs we use have SPARSEMEM_VMEMMAP enabled.
>
> Interesting... we have config ARCH_SPARSEMEM_ENABLE depend on !XEN at
> SUSE. Figured this was a generic issue. The SUSE kernels are based on
> 3.12 though, but anyway with it enabled I do get compile failures
> because of redefinition of MAX_PHYSMEM_BITS which we provide on Xen
> set to 43 for some reason (can't find that justification), so it
> doesn't use the default 46 that would be used otherwise. But another
> reason seems to be the lack of forward porting yet PAT support for PV
> domains -- commit 47591df50 upstream which requires us to still have
> the union on the pte_t, and I suppose we need ca15f20f as well...
>
> If there is nothing else I suppose this just requires fixing up at
> SUSE's end for SPARSEMEM_VMEMMAP...

The SUSE kernel has several patches renaming/altering Xen-related config
options. Don't mix that up with upstream/pvops.

Juergen
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