linux-kernel - Re: [PATCH v11 1/6] kasan: allow an architecture to disable inline instrumentation

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Date:   Mon, 22 Mar 2021 22:08:05 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Daniel Axtens <dja@...ens.net>,
        Balbir Singh <bsingharora@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, kasan-dev@...glegroups.com,
        christophe.leroy@...roup.eu, aneesh.kumar@...ux.ibm.com
Subject: Re: [PATCH v11 1/6] kasan: allow an architecture to disable inline
 instrumentation

Daniel Axtens <dja@...ens.net> writes:
> Balbir Singh <bsingharora@...il.com> writes:
>
>> On Sat, Mar 20, 2021 at 01:40:53AM +1100, Daniel Axtens wrote:
>>> For annoying architectural reasons, it's very difficult to support inline
>>> instrumentation on powerpc64.
>>
>> I think we can expand here and talk about how in hash mode, the vmalloc
>> address space is in a region of memory different than where kernel virtual
>> addresses are mapped. Did I recollect the reason correctly?
>
> I think that's _a_ reason, but for radix mode (which is all I support at
> the moment), the reason is a bit simpler.

Actually Aneesh fixed that in:

  0034d395f89d ("powerpc/mm/hash64: Map all the kernel regions in the same 0xc range")

The problem we had prior to that was that the linear mapping was at
(0xc << 60), vmalloc was at (0xd << 60), and vmemap was at (0xf << 60).

Meaning our shadow region would need to be more than (3 << 60) in size.

cheers