Re: [PATCH v5 06/19] arm64: realm: Query IPA size from the RMM

[Gavin Shan <gshan@redhat.com>]

On 8/19/24 11:19 PM, 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 v4:
>   * Make PROT_NS_SHARED check is_realm_world() to reduce impact on
>     non-CCA systems.
> 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 | 4 ++++
>   arch/arm64/kernel/rsi.c               | 8 ++++++++
>   2 files changed, 12 insertions(+)
> 

One nit below.

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index b11cfb9fdd37..5e578274a3b7 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -68,8 +68,12 @@
>   
>   #include <asm/cpufeature.h>
>   #include <asm/pgtable-types.h>
> +#include <asm/rsi.h>
>   
>   extern bool arm64_use_ng_mappings;
> +extern unsigned long prot_ns_shared;
> +
> +#define PROT_NS_SHARED		(is_realm_world() ? prot_ns_shared : 0)
>   
>   #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 128a9a05a96b..e968a5c9929e 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);
>   
> @@ -72,6 +77,9 @@ 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);
>   }

Nit: It's probably worthy to warn on errors returned from rsi_get_realm_config(),
It's hard to debug and follow if it fails silently.

Thanks,
Gavin