linux-kernel - Re: [PATCH 1/5] KVM: arm64: Drop direct PAGE

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Message-ID: <7ac63cc6-d35a-d455-f629-abea2932d312@arm.com>
Date:   Wed, 11 Aug 2021 11:02:05 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] KVM: arm64: Drop direct PAGE_[SHIFT|SIZE] usage as
 page size



On 8/10/21 6:50 PM, Will Deacon wrote:
> On Tue, Aug 10, 2021 at 12:32:37PM +0530, Anshuman Khandual wrote:
>> All instances here could just directly test against CONFIG_ARM64_XXK_PAGES
>> instead of evaluating via PAGE_SHIFT or PAGE_SIZE. With this change, there
>> will be no such usage left.
>>
>> Cc: Marc Zyngier <maz@...nel.org>
>> Cc: James Morse <james.morse@....com>
>> Cc: Alexandru Elisei <alexandru.elisei@....com>
>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: kvmarm@...ts.cs.columbia.edu
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>  arch/arm64/kvm/hyp/pgtable.c | 6 +++---
>>  arch/arm64/mm/mmu.c          | 2 +-
>>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> Why is this better?

There are two improvements here.

1. Avoids using hard coded numerical shift values to determine the page size

	e.g PAGE_SHIFT = 16 for 64K

2. There are already instances of IS_ENABLED() construct checking for the page
   size. After this change there will be just a single method to test page size
   , rather than checking for either config, PAGE_SHIFT or PAGE_SIZE etc through
   out arm64. This change helps in that unification around IS_ENABLED().

There is another patch which drops remaining usage for PAGE_SIZE as well.

https://patchwork.kernel.org/project/linux-arm-kernel/patch/1628569782-30213-1-git-send-email-anshuman.khandual@arm.com/