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Date: Wed, 8 Jan 2020 10:04:54 -0600
From: Tianlin Li <tli@...italocean.com>
To: Christian König <christian.koenig@....com>
Cc: kernel-hardening@...ts.openwall.com,
 keescook@...omium.org,
 Alex Deucher <alexander.deucher@....com>,
 David1.Zhou@....com,
 David Airlie <airlied@...ux.ie>,
 Daniel Vetter <daniel@...ll.ch>,
 amd-gfx@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] drm/radeon: have the callers of set_memory_*() check
 the return value


> On Jan 8, 2020, at 6:56 AM, Christian König <christian.koenig@....com> wrote:
> 
> Am 07.01.20 um 20:25 schrieb Tianlin Li:
>> Right now several architectures allow their set_memory_*() family of
>> functions to fail, but callers may not be checking the return values.
>> If set_memory_*() returns with an error, call-site assumptions may be
>> infact wrong to assume that it would either succeed or not succeed at
>> all. Ideally, the failure of set_memory_*() should be passed up the
>> call stack, and callers should examine the failure and deal with it.
>> 
>> Need to fix the callers and add the __must_check attribute. They also
>> may not provide any level of atomicity, in the sense that the memory
>> protections may be left incomplete on failure. This issue likely has a
>> few steps on effects architectures:
>> 1)Have all callers of set_memory_*() helpers check the return value.
>> 2)Add __must_check to all set_memory_*() helpers so that new uses do
>> not ignore the return value.
>> 3)Add atomicity to the calls so that the memory protections aren't left
>> in a partial state.
>> 
>> This series is part of step 1. Make drm/radeon check the return value of
>> set_memory_*().
> 
> I'm a little hesitate merge that. This hardware is >15 years old and nobody of the developers have any system left to test this change on.
> 
> Would it be to much of a problem to just add something like: r = set_memory_*(); (void)r; /* Intentionally ignored */.

Thank you. I will fix that in patch 1 and remove patch 2 (since no need to fix the call sites to handle the retval). 

Best regards,
Tianlin
> Apart from that certainly a good idea to add __must_check to the functions.
> 
> Regards,
> Christian.
> 
>> 
>> Tianlin Li (2):
>>   drm/radeon: have the callers of set_memory_*() check the return value
>>   drm/radeon: change call sites to handle return value properly.
>> 
>>  drivers/gpu/drm/radeon/r100.c        |  3 ++-
>>  drivers/gpu/drm/radeon/radeon.h      |  2 +-
>>  drivers/gpu/drm/radeon/radeon_gart.c | 22 ++++++++++++++++++----
>>  drivers/gpu/drm/radeon/rs400.c       |  3 ++-
>>  4 files changed, 23 insertions(+), 7 deletions(-)


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