linux-kernel - Re: [PATCH 0/4] x86/mm/cpa: Fix cpa-array TLB invalidation

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Date:   Wed, 5 Dec 2018 16:24:02 +0000
From:   "StDenis, Tom" <Tom.StDenis@....com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "Koenig, Christian" <Christian.Koenig@....com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Deucher, Alexander" <Alexander.Deucher@....com>
Subject: Re: [PATCH 0/4] x86/mm/cpa: Fix cpa-array TLB invalidation

Hi Peter,

Good news is that I got our opengl test running on your x86/mm branch. 
The commit a2b4306c50b5de2ca955cd73ac57c2ac6426ee15 (current tip of 
x86/mm) is good.  For sanity I jumped back and found  this commit
a2aa52ab16efbee40ad118ebac4a5e438f5b43ee doesn't work.

Thanks,
Tom



On 2018-12-03 2:26 p.m., Tom St Denis wrote:
> Hi Peter,
> 
> After updating my UMDs (mesa/etc) over the weekend I cannot reproduce 
> the bug to begin with.  I'll try jumping directly to the intersection 
> and see if I can reproduce the fault there otherwise I'll have to 
> rollback my umds.
> 
> Hopefully I can test this tomorrow.
> 
> Tom
> 
> On 2018-12-03 10:41 a.m., Peter Zijlstra wrote:
>> On Fri, Nov 30, 2018 at 04:19:46PM +0000, StDenis, Tom wrote:
>>> NAK I get a failure in TTM on init with your x86/mm branch (see attached
>>> dmesg).
>>
>> So the good news is that with some additional self-tests I can trivially
>> reproduce this. The bad news is that an otherwise straight forward
>> cleanup seems to make CPA horribly mad at me.
>>
>> And since we're somewhat late in the release cycle, I suppose we should
>> do the simple thing first, and then I can try and figure out this CPA
>> mess later.
>>
>> So how about this relatively simple partial revert to sort the problem.
>>
>> ---
>> Subject: x86/mm/cpa: Fix cpa_flush_array() TLB invalidation
>>
>> In commit:
>>
>>    a7295fd53c39 ("x86/mm/cpa: Use flush_tlb_kernel_range()")
>>
>> I misread the cpa array code and incorrectly used
>> tlb_flush_kernel_range(), resulting in missing TLB flushes and
>> consequent failures.
>>
>> Instead do a full invalidate in this case -- for now.
>>
>> Fixes: a7295fd53c39 ("x86/mm/cpa: Use flush_tlb_kernel_range()")
>> Reported-by: "StDenis, Tom" <Tom.StDenis@....com>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>> ---
>>   arch/x86/mm/pageattr.c | 24 ++++++++++++++++--------
>>   1 file changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
>> index bac35001d896..61bc7d1800d7 100644
>> --- a/arch/x86/mm/pageattr.c
>> +++ b/arch/x86/mm/pageattr.c
>> @@ -285,20 +285,16 @@ static void cpa_flush_all(unsigned long cache)
>>       on_each_cpu(__cpa_flush_all, (void *) cache, 1);
>>   }
>> -static bool __cpa_flush_range(unsigned long start, int numpages, int 
>> cache)
>> +static bool __inv_flush_all(int cache)
>>   {
>>       BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
>> -    WARN_ON(PAGE_ALIGN(start) != start);
>> -
>>       if (cache && !static_cpu_has(X86_FEATURE_CLFLUSH)) {
>>           cpa_flush_all(cache);
>>           return true;
>>       }
>> -    flush_tlb_kernel_range(start, start + PAGE_SIZE * numpages);
>> -
>> -    return !cache;
>> +    return false;
>>   }
>>   static void cpa_flush_range(unsigned long start, int numpages, int 
>> cache)
>> @@ -306,7 +302,14 @@ static void cpa_flush_range(unsigned long start, 
>> int numpages, int cache)
>>       unsigned int i, level;
>>       unsigned long addr;
>> -    if (__cpa_flush_range(start, numpages, cache))
>> +    WARN_ON(PAGE_ALIGN(start) != start);
>> +
>> +    if (__inv_flush_all(cache))
>> +        return;
>> +
>> +    flush_tlb_kernel_range(start, start + PAGE_SIZE * numpages);
>> +
>> +    if (!cache)
>>           return;
>>       /*
>> @@ -332,7 +335,12 @@ static void cpa_flush_array(unsigned long baddr, 
>> unsigned long *start,
>>   {
>>       unsigned int i, level;
>> -    if (__cpa_flush_range(baddr, numpages, cache))
>> +    if (__inv_flush_all(cache))
>> +        return;
>> +
>> +    flush_tlb_all();
>> +
>> +    if (!cache)
>>           return;
>>       /*
>>
>