linux-kernel - Re: [PATCH 01/10] mm: Move common parts of pagetable_*

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Message-ID: <0daabd32-cba4-4345-baa8-e8c66bc899ff@bytedance.com>
Date: Fri, 20 Dec 2024 19:46:04 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Catalin Marinas <catalin.marinas@....com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Linus Walleij <linus.walleij@...aro.org>, Andy Lutomirski <luto@...nel.org>,
 "Mike Rapoport (IBM)" <rppt@...nel.org>, Ryan Roberts
 <ryan.roberts@....com>, Thomas Gleixner <tglx@...utronix.de>,
 Will Deacon <will@...nel.org>, Matthew Wilcox <willy@...radead.org>,
 linux-alpha@...r.kernel.org, linux-arch@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
 linux-hexagon@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
 linux-openrisc@...r.kernel.org, linux-parisc@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
 linux-snps-arc@...ts.infradead.org, linux-um@...ts.infradead.org,
 loongarch@...ts.linux.dev, x86@...nel.org,
 Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH 01/10] mm: Move common parts of pagetable_*_[cd]tor to
 helpers

Hi Kevin,

On 2024/12/20 18:49, Kevin Brodsky wrote:
> Hi Peter, Qi,
> 
> On 19/12/2024 18:19, Peter Zijlstra wrote:
>> On Thu, Dec 19, 2024 at 04:44:16PM +0000, Kevin Brodsky wrote:
>>> Besides the ptlock management at PTE/PMD level, all the
>>> pagetable_*_[cd]tor have the same implementation. Introduce common
>>> helpers for all levels to reduce the duplication.
>> Uff, I forgot to Cc you on the discussion here, sorry!:
>>
>>    https://lkml.kernel.org/r/cover.1734526570.git.zhengqi.arch@bytedance.com
>>
>> we now have two series doing more or less overlapping things :/
>>
>> You can in fact trivially merge the all the implementations -- the
>> apparent non-common bit (ptlock_free) is a no-op for all those other
>> levels because they'll be having ptdesc->lock == NULL.
> 
> Ah that is good to know, thanks for letting me know about that and Qi's
> series! Fortunately there isn't that much overlap between our series - I
> think we can easily sort this out.
> 
> Qi, shall we collaborate to make our series complementary? I believe my
> series covers patch 2 and 4 of your series, but it goes further by
> covering all levels and all architectures, and patches introducing
> ctor/dtor are already split as Alexander suggested on your series. So my
> suggestion would be:
> 
> * Remove patch 1 in my series - I'd just introduce
> pagetable_{p4d,pgd}_[cd]tor with the same implementation as
> pagetable_pud_[cd]tor.
> * Remove patch 2 and 4 from your series and rebase it on mine.

I quickly went through your patch series. It looks like my patch 2 and
your patch 6 are duplicated, so you want me to remove my patch 2.

But I think you may not be able to simple let arm64, riscv and x86 to
use generic p4d_{alloc_one,free}(). Because even if
CONFIG_PGTABLE_LEVELS > 4, the pgtable_l5_enabled() may not be true.

For example, in arm64:

#if CONFIG_PGTABLE_LEVELS > 4

static __always_inline bool pgtable_l5_enabled(void)
{
	if (!alternative_has_cap_likely(ARM64_ALWAYS_BOOT))
		return vabits_actual == VA_BITS;
	return alternative_has_cap_unlikely(ARM64_HAS_VA52);
}

Did I miss something?

My patch series is not only for cleanup, but also for fixes of
UAF issue [1], so is it possible to rebase your patch series onto
mine? I can post v3 ASAP.

[1]. 
https://lore.kernel.org/all/67548279.050a0220.a30f1.015b.GAE@google.com/

Thanks!

> 
> Let me know if that makes sense, if so I'll post a v2.
> 
> Cheers,
> - Kevin