linux-kernel - Re: [PATCH 3/4] arm64: mm: support large block mapping when rodata=full

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Message-ID: <ac76c5f5-ead1-4d17-9ef0-0f8068cf8d8d@arm.com>
Date: Mon, 4 Aug 2025 11:07:25 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Yang Shi <yang@...amperecomputing.com>, will@...nel.org,
 catalin.marinas@....com, akpm@...ux-foundation.org, Miko.Lenczewski@....com,
 dev.jain@....com, scott@...amperecomputing.com, cl@...two.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] arm64: mm: support large block mapping when
 rodata=full

On 01/08/2025 15:35, Ryan Roberts wrote:

[...]

>> @@ -1366,7 +1648,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>>  
>>  	VM_BUG_ON(!mhp_range_allowed(start, size, true));
>>  
>> -	if (can_set_direct_map())
>> +	if (force_pte_mapping() ||
>> +	    (linear_map_requires_bbml2 && !system_supports_bbml2_noabort()))
> 
> So force_pte_mapping() isn't actually returning what it sounds like it is; it's
> returning whether you would have to force pte mapping based on the current cpu's
> support for bbml2. Perhaps it would be better to implement force_pte_mapping()  as:
> 
> static inline bool force_pte_mapping(void)
> {
> 	bool bbml2 = (system_capabilities_finalized() &&
> 			system_supports_bbml2_noabort()) ||
> 			bbml2_noabort_available();

Sorry that should have been:

	bool bbml2 = system_capabilities_finalized() ?
		system_supports_bbml2_noabort() : bbml2_noabort_available();

> 
> 	return (!bbml2 && (rodata_full || arm64_kfence_can_set_direct_map() ||
> 			   is_realm_world())) ||
> 		debug_pagealloc_enabled();
> }