linux-kernel - Re: [PATCH] powerpc: align memory_limit to 16MB in early_parse

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Date: Mon, 4 Mar 2024 12:28:23 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
To: Michael Ellerman <mpe@...erman.id.au>, Joel Savitz <jsavitz@...hat.com>,
 linux-kernel@...r.kernel.org
Cc: Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 Benjamin Gray <bgray@...ux.ibm.com>, Paul Mackerras <paulus@...abs.org>,
 linuxppc-dev@...ts.ozlabs.org, Gonzalo Siero <gsierohu@...hat.com>
Subject: Re: [PATCH] powerpc: align memory_limit to 16MB in early_parse_mem

On 3/2/24 4:53 AM, Michael Ellerman wrote:
> Hi Joel,
> 
> Joel Savitz <jsavitz@...hat.com> writes:
>> On 64-bit powerpc, usage of a non-16MB-aligned value for the mem= kernel
>> cmdline parameter results in a system hang at boot.
> 
> Can you give us any more details on that? It might be a bug we can fix.
> 
>> For example, using 'mem=4198400K' will always reproduce this issue.
>>
>> This patch fixes the problem by aligning any argument to mem= to 16MB
>> corresponding with the large page size on powerpc.
> 
> The large page size depends on the MMU, with Radix it's 2MB or 1GB. So
> depending on what's happening 16MB may not be enough.
> 
> What system are you testing on?
> 

htab_bolt_mapping should have aligned things to a lower value that is 16MB aligned.

	/* Carefully map only the possible range */
	vaddr = ALIGN(vstart, step);
	paddr = ALIGN(pstart, step);
	vend  = ALIGN_DOWN(vend, step);

-aneesh