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@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.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)
 
 #define PTE_MAYBE_NG		(arm64_use_ng_mappings ? PTE_NG : 0)
 #define PMD_MAYBE_NG		(arm64_use_ng_mappings ? PMD_SECT_NG : 0)
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index f01bff9dab04..231c1a3ecdeb 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -8,6 +8,11 @@
 #include <linux/psci.h>
 #include <asm/rsi.h>
 
+struct realm_config config;
+
+unsigned long prot_ns_shared;
+EXPORT_SYMBOL(prot_ns_shared);
+
 DEFINE_STATIC_KEY_FALSE_RO(rsi_present);
 EXPORT_SYMBOL(rsi_present);
 
@@ -71,6 +76,9 @@ void __init arm64_rsi_init(void)
 		return;
 	if (!rsi_version_matches())
 		return;
+	if (rsi_get_realm_config(&config))
+		return;
+	prot_ns_shared = BIT(config.ipa_bits - 1);
 
 	static_branch_enable(&rsi_present);
 }
-- 
2.34.1

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@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.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?

Will

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@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> Signed-off-by: Steven Price <steven.price@arm.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