linux-kernel - Re: [PATCH] arm64: uprobes: Optimize cache flushes for xol slot

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Message-ID: <Zy0IjTkqlCZ9DRWN@arm.com>
Date: Thu, 7 Nov 2024 18:35:57 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: "Liao, Chang" <liaochang1@...wei.com>
Cc: mhiramat@...nel.org, oleg@...hat.com, peterz@...radead.org,
	will@...nel.org, mark.rutland@....com, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: uprobes: Optimize cache flushes for xol slot

On Wed, Nov 06, 2024 at 05:55:16PM +0800, Liao, Chang wrote:
> 在 2024/9/19 20:17, Liao Chang 写道:
> > On 09/23, Will Deacon wrote:
> >> However, we should use __GFP_ZERO anyway
> >> because I don't think it's a good idea to map an uninitialised page into
> >> userspace.
> > Agreed, and imo this even needs a separate "fix info leak" patch.
> > 
> > Oleg.
> 
> Given that Oleg's fix info leak patch has been merged [1], the risk of leakage
> is gone. So I am looking forward to your options about this patch. As many
> functions start with same instructions like 'stp fp, lr, [sp, #imm]' or
> 'paciasp'. So I think this patch could avoid unnecessary D/I cache synchronization.
> 
> [1] https://lore.kernel.org/all/20240929162047.GA12611@redhat.com/

The patch is fine with the fix in __create_xol_area(). But please add a
comment on why it is safe to skip the cache maintenance, something like
"the initial cache maintenance was done via set_pte_at()" (well, I can
do this when applying).

-- 
Catalin