linux-kernel - Re: [PATCH v9 3/8] KVM: arm/arm64: Introduce helpers to manipulate page table entries

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Date:   Mon, 3 Dec 2018 14:03:11 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        Punit Agrawal <punit.agrawal@....com>,
        kvmarm@...ts.cs.columbia.edu
Cc:     marc.zyngier@....com, Catalin Marinas <catalin.marinas@....com>,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        Russell King <linux@...linux.org.uk>, punitagrawal@...il.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 3/8] KVM: arm/arm64: Introduce helpers to manipulate
 page table entries

Hi Anshuman,

On 03/12/2018 13:50, Anshuman Khandual wrote:
> 
> 
> On 10/31/2018 11:27 PM, Punit Agrawal wrote:
>> Introduce helpers to abstract architectural handling of the conversion
>> of pfn to page table entries and marking a PMD page table entry as a
>> block entry.
> 
> Why is this necessary ? we would still need to access PMD, PUD as is
> without any conversion. IOW KVM knows the breakdown of the page table
> at various levels. Is this something required from generic KVM code ?

The KVM MMU code is shared for arm32 and arm64. Hence we need arch specific
helpers to hide how we deal with the levels. e.g, PUD never exists for
arm32.

>    
>>
>> The helpers are introduced in preparation for supporting PUD hugepages
>> at stage 2 - which are supported on arm64 but do not exist on arm.
> 
> Some of these patches (including the earlier two) are good on it's
> own. Do we have still mention in commit message about the incoming PUD
> enablement as the reason for these cleanup patches ?
> 

Cheers
Suzuki