linux-kernel - Re: [PATCH v4 04/15] arm64: realm: Query IPA size from the RMM

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Message-ID: <b6dc6c3a-cbf1-406f-a885-48eebf0c3d78@arm.com>
Date: Wed, 10 Jul 2024 16:34:15 +0100
From: Steven Price <steven.price@....com>
To: Will Deacon <will@...nel.org>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
 Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 James Morse <james.morse@....com>, Oliver Upton <oliver.upton@...ux.dev>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Joey Gouly <joey.gouly@....com>,
 Alexandru Elisei <alexandru.elisei@....com>,
 Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v4 04/15] arm64: realm: Query IPA size from the RMM

On 09/07/2024 11:53, Will Deacon wrote:
> On Mon, Jul 01, 2024 at 10:54:54AM +0100, Steven Price wrote:
>> The top bit of the configured IPA size is used as an attribute to
>> control whether the address is protected or shared. Query the
>> configuration from the RMM to assertain which bit this is.
>>
>> Co-developed-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Signed-off-by: Steven Price <steven.price@....com>
>> ---
>> Changes since v2:
>>  * Drop unneeded extra brackets from PROT_NS_SHARED.
>>  * Drop the explicit alignment from 'config' as struct realm_config now
>>    specifies the alignment.
>> ---
>>  arch/arm64/include/asm/pgtable-prot.h | 3 +++
>>  arch/arm64/kernel/rsi.c               | 8 ++++++++
>>  2 files changed, 11 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
>> index b11cfb9fdd37..6c29f3b32eba 100644
>> --- a/arch/arm64/include/asm/pgtable-prot.h
>> +++ b/arch/arm64/include/asm/pgtable-prot.h
>> @@ -70,6 +70,9 @@
>>  #include <asm/pgtable-types.h>
>>  
>>  extern bool arm64_use_ng_mappings;
>> +extern unsigned long prot_ns_shared;
>> +
>> +#define PROT_NS_SHARED		(prot_ns_shared)
> 
> Since the _vast_ majority of Linux systems won't be running in a realm,
> can we use a static key to avoid loading a constant each time?

Fair enough, the following should do the trick:

#define PROT_NS_SHARED		(is_realm_world() ? prot_ns_shared : 0)

Thanks,
Steve