linux-kernel - Re: [PATCH v4 12/14] x86: Add KHO support

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Message-ID: <Z7yD9g1AgtUUfKr0@kernel.org>
Date: Mon, 24 Feb 2025 16:36:38 +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 12/14] x86: Add KHO support

On Mon, Feb 24, 2025 at 07:13:55AM +0000, Wei Yang wrote:
> On Thu, Feb 06, 2025 at 03:27:52PM +0200, Mike Rapoport wrote:
> >From: Alexander Graf <graf@...zon.com>
> [...]
> >diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> >index 82b96ed9890a..0b81cd70b02a 100644
> >--- a/arch/x86/kernel/e820.c
> >+++ b/arch/x86/kernel/e820.c
> >@@ -1329,6 +1329,24 @@ void __init e820__memblock_setup(void)
> > 		memblock_add(entry->addr, entry->size);
> > 	}
> > 
> >+	/*
> >+	 * At this point with KHO we only allocate from scratch memory.
> >+	 * At the same time, we configure memblock to only allow
> >+	 * allocations from memory below ISA_END_ADDRESS which is not
> >+	 * a natural scratch region, because Linux ignores memory below
> >+	 * ISA_END_ADDRESS at runtime. Beside very few (if any) early
> >+	 * allocations, we must allocate real-mode trapoline below
> >+	 * ISA_END_ADDRESS.
> >+	 *
> >+	 * To make sure that we can actually perform allocations during
> >+	 * this phase, let's mark memory below ISA_END_ADDRESS as scratch
> >+	 * so we can allocate from there in a scratch-only world.
> >+	 *
> >+	 * After real mode trampoline is allocated, we clear scratch
> >+	 * marking from the memory below ISA_END_ADDRESS
> >+	 */
> >+	memblock_mark_kho_scratch(0, ISA_END_ADDRESS);
> >+
> 
> At the beginning of e820__memblock_setup() we call memblock_allow_resize(),
> which means during adding memory region it could double the array. And the
> memory used here is from some region just added.

There are large KHO scratch areas that will be used for most allocations.
Marking the memory below ISA_END_ADDRESS as KHO scratch is required to
satisfy allocations that explicitly limit the allocation to ISA_END_ADDRESS,
e.g the real time trampoline.
 
> But with KHO, I am afraid it would fail?
> 
> > 	/* Throw away partial pages: */
> > 	memblock_trim_memory(PAGE_SIZE);
> > 
> 
> -- 
> Wei Yang
> Help you, Help me

-- 
Sincerely yours,
Mike.