linux-kernel - Re: [PATCH] riscv: Don't use hugepage mappings for vmemmap if it's not supported

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Message-ID: <8b741144-8a3c-4a4c-bb3f-dfab4aa8e576@ghiti.fr>
Date: Fri, 24 May 2024 22:07:40 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Nam Cao <namcao@...utronix.de>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alexghiti@...osinc.com>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Don't use hugepage mappings for vmemmap if it's
 not supported

Hi Nam,

On 08/05/2024 20:46, Nam Cao wrote:
> On Wed, May 08, 2024 at 08:22:43PM +0200, Alexandre Ghiti wrote:
>> Hi Nam,
> Hi Alex,
>
>>> Commit ff172d4818ad ("riscv: Use hugepage mappings for vmemmap") broke XIP
>>> kernel, because huge pages are not supported on XIP kernel.
>> I don't understand why XIP kernels can't support huge vmalloc mappings,
> Me neither.
>
>> so I
>> think the right fix would be to enable such mappings on XIP. WDYT?
> I agree that is the ideal solution. But I don't want to send any new
> feature to the stable trees (stable folks may even reject such patch).
> So I intend that to be in another patch.


I have been thinking about that, and I actually think that the real fix 
is enabling huge vmalloc mappings for XIP as it was an oversight/mistake 
in the first place. On 64-bit kernels, there are no reasons we can't use 
PMD mappings for vmalloc. So I'd rather not go with this fix.

Thanks,

Alex


>
> Best regards,
> Nam