Re: [PATCH v3 00/21] KVM: arm64: Rewrite page-table code and fault handling

From: Marc Zyngier <maz@kernel.org>
To: Gavin Shan <gshan@redhat.com>
Cc: kernel-team@android.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 00/21] KVM: arm64: Rewrite page-table code and fault handling
Date: Fri, 04 Sep 2020 11:07:50 +0100	[thread overview]
Message-ID: <fa494886b9a88ec7b02141f2da44d5a7@kernel.org> (raw)
In-Reply-To: <5aa43d21-30a1-68c8-2620-60a25e4edfa2@redhat.com>

On 2020-09-04 01:51, Gavin Shan wrote:
> Hi Will,
> 
> On 9/3/20 10:16 PM, Will Deacon wrote:
>> On Thu, Sep 03, 2020 at 09:48:18PM +1000, Gavin Shan wrote:
>>> On 9/3/20 9:13 PM, Gavin Shan wrote:
>>>> On 9/3/20 5:34 PM, Gavin Shan wrote:
>>>>> On 8/25/20 7:39 PM, Will Deacon wrote:
>>>>>> Hello folks,
>>>>>> 
>>>>>> This is version three of the KVM page-table rework that I 
>>>>>> previously posted
>>>>>> here:
>>>>>> 
>>>>>>     v1: 
>>>>>> https://lore.kernel.org/r/20200730153406.25136-1-will@kernel.org
>>>>>>     v2: 
>>>>>> https://lore.kernel.org/r/20200818132818.16065-1-will@kernel.org
>>>>>> 
>>>>>> Changes since v2 include:
>>>>>> 
>>>>>>     * Rebased onto -rc2, which includes the conflicting OOM 
>>>>>> blocking fixes
>>>>>>     * Dropped the patch trying to "fix" the memcache in 
>>>>>> kvm_phys_addr_ioremap()
>>>>>> 
>>>>> 
>>>>> It's really nice work, making the code unified/simplified greatly.
>>>>> However, it seems it doesn't work well with HugeTLBfs. Please refer
>>>>> to the following test result and see if you have quick idea, or I
>>>>> can debug it a bit :)
>> 
>> Nice testing matrix, and thanks for reporting the problem!
>> 
>>>>> Machine         Host                     Guest              Result
>>>>> ===============================================================
>>>>> ThunderX2    VA_BITS:   42           PAGE_SIZE:  4KB     Passed
>>>>>                PAGE_SIZE: 64KB                    64KB     passed
>>>>>                THP:       disabled
>>>>>                HugeTLB:   disabled
>>>>> ---------------------------------------------------------------
>>>>> ThunderX2    VA_BITS:   42           PAGE_SIZE:  4KB     Passed
>>>>>                PAGE_SIZE: 64KB                    64KB     passed
>>>>>                THP:       enabled
>>>>>                HugeTLB:   disabled
>>>>> ----------------------------------------------------------------
>>>>> ThunderX2    VA_BITS:   42           PAGE_SIZE:  4KB     Fail[1]
>>>>>                PAGE_SIZE: 64KB                    64KB     Fail[1]
>>>>>                THP:       disabled
>>>>>                HugeTLB:   enabled
>>>>> ---------------------------------------------------------------
>>>>> ThunderX2    VA_BITS:   39           PAGE_SIZE:  4KB     Passed
>>>>>                PAGE_SIZE: 4KB                     64KB     Passed
>>>>>                THP:       disabled
>>>>>                HugeTLB:   disabled
>>>>> ---------------------------------------------------------------
>>>>> ThunderX2    VA_BITS:   39           PAGE_SIZE:  4KB     Passed
>>>>>                PAGE_SIZE: 4KB                     64KB     Passed
>>>>>                THP:       enabled
>>>>>                HugeTLB:   disabled
>>>>> --------------------------------------------------------------
>>>>> ThunderX2    VA_BITS:   39           PAGE_SIZE: 4KB     Fail[2]
>>>>>                PAGE_SIZE: 4KB                    64KB     Fail[2]
>>>>>                THP:       disabled
>>>>>                HugeTLB:   enabled
>>>>> 
>>>> 
>>>> I debugged the code and found the issue is caused by the following
>>>> patch.
>>>> 
>>>> [PATCH v3 06/21] KVM: arm64: Add support for stage-2 map()/unmap() 
>>>> in generic page-table
>> 
>> (I think this is just a symptom of the page-table being out of whack)
>> 
>>> Sorry that the guest could hang sometimes with above changes. I have 
>>> no idea what
>>> has been happening before I'm going to debug for more.. I'm pasting 
>>> the used command
>>> and output from guest.
>> 
>> Can you try the diff below, please? I think we can end up sticking 
>> down a
>> huge-page-sized mapping at an unaligned address, which causes us both 
>> to
>> overmap and also to fail to use the huge granule for a block mapping.
>> 
> 
> Since the the following changes have been folded to v4, I reran the 
> test cases
> on v4 and everything works fine.

Thanks a lot for the great testing and reviewing effort!

<shameless ask>
Since you obviously have a test rig setup for this: does your TX2 
support 16kB
pages? If so, could you please do another run with this page size on the 
host?
</shameless ask>

Thanks again,

         M.
-- 
Jazz is not dead. It just smells funny...
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