From: Will Deacon <will@kernel.org>
To: Yang Shi <yang@os.amperecomputing.com>
Cc: catalin.marinas@arm.com, cl@gentwo.org,
scott@os.amperecomputing.com,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/3] arm64: support FEAT_BBM level 2 and large block mapping when rodata=full
Date: Tue, 10 Dec 2024 11:31:52 +0000 [thread overview]
Message-ID: <20241210113151.GC14735@willie-the-truck> (raw)
In-Reply-To: <20241118181711.962576-1-yang@os.amperecomputing.com>
On Mon, Nov 18, 2024 at 10:16:07AM -0800, Yang Shi wrote:
>
> When rodata=full kernel linear mapping is mapped by PTE due to arm's
> break-before-make rule.
>
> This resulted in a couple of problems:
> - performance degradation
> - more TLB pressure
> - memory waste for kernel page table
>
> There are some workarounds to mitigate the problems, for example, using
> rodata=on, but this compromises the security measurement.
>
> With FEAT_BBM level 2 support, splitting large block page table to
> smaller ones doesn't need to make the page table entry invalid anymore.
> This allows kernel split large block mapping on the fly.
I think you can still get TLB conflict aborts in this case, so this
doesn't work. Hopefully the architecture can strengthen this in the
future to give you what you need.
Will
next prev parent reply other threads:[~2024-12-10 11:34 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-18 18:16 [RFC PATCH 0/3] arm64: support FEAT_BBM level 2 and large block mapping when rodata=full Yang Shi
2024-11-18 18:16 ` [PATCH 1/3] arm64: cpufeature: detect FEAT_BBM level 2 Yang Shi
2024-11-18 18:16 ` [PATCH 2/3] arm64: mm: support large block mapping when rodata=full Yang Shi
2024-11-18 18:16 ` [PATCH 3/3] arm64: cpufeature: workaround AmpereOne FEAT_BBM level 2 Yang Shi
2024-11-18 18:33 ` Christoph Lameter (Ampere)
2024-12-02 23:39 ` [RFC PATCH 0/3] arm64: support FEAT_BBM level 2 and large block mapping when rodata=full Yang Shi
2024-12-10 11:31 ` Will Deacon [this message]
2024-12-10 19:33 ` Yang Shi
2024-12-11 22:30 ` Will Deacon
2024-12-12 0:05 ` Yang Shi
2024-12-11 17:24 ` Christoph Lameter (Ampere)
2025-01-02 12:13 ` Jonathan Cameron
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