linux-kernel - Re: [PATCH v2 0/1] Accept unaccepted kexec segments' destination addresses

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Message-ID: <wk7tfjqtpzgmsvilgszlgqnqjgm5kg2vfxboaspd3qyfs6uqb3@nbgacwb3kcb6>
Date: Tue, 4 Mar 2025 10:41:56 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: akpm@...ux-foundation.org, "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Dave Hansen <dave.hansen@...el.com>, Baoquan He <bhe@...hat.com>, 
	"Kirill A. Shutemov" <kirill@...temov.name>, kexec@...ts.infradead.org, Yan Zhao <yan.y.zhao@...el.com>, 
	linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, x86@...nel.org, 
	rick.p.edgecombe@...el.com, security@...nel.org
Subject: Re: [PATCH v2 0/1] Accept unaccepted kexec segments' destination
 addresses

On Fri, Feb 14, 2025 at 08:20:07AM -0800, Dave Hansen wrote:
> On 2/14/25 05:46, Kirill A. Shutemov wrote:
> >> It sounds like you're advocating for the "slow guest boot" option.
> >> Kirill, can you remind us how fast a guest boots to the shell for
> >> modestly-sized (say 256GB) memory with "accept_memory=eager" versus
> >> "accept_memory=lazy"? IIRC, it was a pretty remarkable difference.
> > I only have 128GB machine readily available and posted some number on
> > other thread[1]:
> > 
> >   On single vCPU it takes about a minute to accept 90GiB of memory.
> > 
> >   It improves a bit with number of vCPUs. It is 40 seconds with 4 vCPU, but
> >   it doesn't scale past that in my setup.
> > 
> > I've mentioned it before in other thread:
> > 
> > [1] https://lore.kernel.org/all/ihzvi5pwn5hrn4ky2ehjqztjxoixaiaby4igmeihqfehy2vrii@tsg6j5qvmyrm
> 
> Oh, wow, from that other thread, you've been trying to get this crash
> fix accepted since November?
> 
> From the looks of it, Eric stopped responding to that thread. I _think_
> you gave a reasonable explanation of why memory acceptance is slow. He
> then popped back up last month raising security concerns. But I don't
> see anyone that shares those concerns.
> 
> The unaccepted memory stuff is also _already_ touching the page
> allocator. If it's a dumb idea, then we should be gleefully ripping it
> out of the page allocator, not rejecting a 2-line kexec patch.
> 
> Baoquan has also said this looks good to him.
> 
> I'm happy to give Eric another week to respond in case he's on vacation
> or something, but I'm honestly not seeing a good reason to hold this bug
> fix up.
> 
> Andrew, is this the kind of thing you can stick into mm and hold on to
> for a bit while we give Eric time to respond?

Andrew, Eric, can we get this patch in?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov