linux-kernel - Re: [PATCH v1 1/6] arm64: Detect the ARMv8.4 TTL feature

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Date:   Wed, 22 Apr 2020 10:13:39 +0800
From:   Zhenyu Ye <yezhenyu2@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Peter Zijlstra <peterz@...radead.org>
CC:     <mark.rutland@....com>, <will@...nel.org>,
        <catalin.marinas@....com>, <aneesh.kumar@...ux.ibm.com>,
        <akpm@...ux-foundation.org>, <npiggin@...il.com>, <arnd@...db.de>,
        <rostedt@...dmis.org>, <maz@...nel.org>, <suzuki.poulose@....com>,
        <tglx@...utronix.de>, <yuzhao@...gle.com>, <Dave.Martin@....com>,
        <steven.price@....com>, <broonie@...nel.org>,
        <guohanjun@...wei.com>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <xiexiangyou@...wei.com>,
        <zhangshaokun@...ilicon.com>, <linux-mm@...ck.org>,
        <arm@...nel.org>, <prime.zeng@...ilicon.com>,
        <kuhn.chenqun@...wei.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v1 1/6] arm64: Detect the ARMv8.4 TTL feature

On 2020/4/22 1:16, Christoph Hellwig wrote:
> On Tue, Apr 21, 2020 at 07:13:28PM +0200, Peter Zijlstra wrote:
>> On Tue, Apr 21, 2020 at 09:53:46AM -0700, Christoph Hellwig wrote:
>>> On Fri, Apr 03, 2020 at 05:00:43PM +0800, Zhenyu Ye wrote:
>>>> From: Marc Zyngier <maz@...nel.org>
>>>>
>>>> In order to reduce the cost of TLB invalidation, the ARMv8.4 TTL
>>>> feature allows TLBs to be issued with a level allowing for quicker
>>>> invalidation.
>>>
>>> What does "issued with a level" mean?
>>
>> What I understood it to be is page-size based on page-table hierarchy.
>> Just like we have on x86, 4k, 2m, 1g etc..
>>
>> So where x86 INVLPG will tear down any sized page for the address given,
>> you can now day, kill me the PMD level translation for @addr.
>>
>> Power9 radix also has things like this.
> 
> Maybe this needs to be spelled out a little more?  The current commit
> log sounds like paper generated by a neural network.
>

Emm... This patch was synchronized from Marc's NV series [1].
"issued with a level" means the TLBs now can get which levels of
page tables the @addr is in. You can also understand it as
page-size as Peter said above, just like pud, pmd, pte...

Anyway, I will explain this in more detail.

Thanks,
Zhenyu