linux-kernel - Re: [PATCH v4 03/14] memblock: Add support for scratch memory

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Message-ID: <Z711oEMpogAHohs8@kernel.org>
Date: Tue, 25 Feb 2025 09:47:44 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: linux-kernel@...r.kernel.org, Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Anthony Yznaga <anthony.yznaga@...cle.com>,
	Arnd Bergmann <arnd@...db.de>, Ashish Kalra <ashish.kalra@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Eric Biederman <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...hat.com>, James Gowans <jgowans@...zon.com>,
	Jonathan Corbet <corbet@....net>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pratyush Yadav <ptyadav@...zon.de>,
	Rob Herring <robh+dt@...nel.org>, Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Lendacky <thomas.lendacky@....com>,
	Usama Arif <usama.arif@...edance.com>,
	Will Deacon <will@...nel.org>, devicetree@...r.kernel.org,
	kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH v4 03/14] memblock: Add support for scratch memory

On Mon, Feb 24, 2025 at 02:50:34AM +0000, Wei Yang wrote:
> On Thu, Feb 06, 2025 at 03:27:43PM +0200, Mike Rapoport wrote:
> >From: Alexander Graf <graf@...zon.com>
> >
> >With KHO (Kexec HandOver), we need a way to ensure that the new kernel
> >does not allocate memory on top of any memory regions that the previous
> >kernel was handing over. But to know where those are, we need to include
> >them in the memblock.reserved array which may not be big enough to hold
> >all ranges that need to be persisted across kexec. To resize the array,
> >we need to allocate memory. That brings us into a catch 22 situation.
> >
> >The solution to that is limit memblock allocations to the scratch regions:
> >safe regions to operate in the case when there is memory that should remain
> >intact across kexec.
> >
> >KHO provides several "scratch regions" as part of its metadata. These
> >scratch regions are contiguous memory blocks that known not to contain any
> >memory that should be persisted across kexec. These regions should be large
> >enough to accommodate all memblock allocations done by the kexeced kernel.
> >
> >We introduce a new memblock_set_scratch_only() function that allows KHO to
> 
> memblock_set_kho_scratch_only?
> 
> >indicate that any memblock allocation must happen from the scratch regions.
> >
> >Later, we may want to perform another KHO kexec. For that, we reuse the
> >same scratch regions. To ensure that no eventually handed over data gets
> >allocated inside a scratch region, we flip the semantics of the scratch
> >region with memblock_clear_scratch_only(): After that call, no allocations
> 
> memblock_clear_kho_scratch_only?

Right, I missed those in the commit message.
 
> >may happen from scratch memblock regions. We will lift that restriction
> >in the next patch.
> >
> 
> -- 
> Wei Yang
> Help you, Help me

-- 
Sincerely yours,
Mike.