Re: [PATCH v6 04/11] arm64: rsi: Add support for checking whether an MMIO is protected

[Gavin Shan <gshan@redhat.com>]

On 10/5/24 12:42 AM, Steven Price wrote:
> From: Suzuki K Poulose <suzuki.poulose@arm.com>
> 
> On Arm CCA, with RMM-v1.0, all MMIO regions are shared. However, in
> the future, an Arm CCA-v1.0 compliant guest may be run in a lesser
> privileged partition in the Realm World (with Arm CCA-v1.1 Planes
> feature). In this case, some of the MMIO regions may be emulated
> by a higher privileged component in the Realm world, i.e, protected.
> 
> Thus the guest must decide today, whether a given MMIO region is shared
> vs Protected and create the stage1 mapping accordingly. On Arm CCA, this
> detection is based on the "IPA State" (RIPAS == RIPAS_IO). Provide a
> helper to run this check on a given range of MMIO.
> 
> Also, provide a arm64 helper which may be hooked in by other solutions.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> New patch for v5
> ---
>   arch/arm64/include/asm/io.h       |  8 ++++++++
>   arch/arm64/include/asm/rsi.h      |  2 ++
>   arch/arm64/include/asm/rsi_cmds.h | 21 +++++++++++++++++++++
>   arch/arm64/kernel/rsi.c           | 26 ++++++++++++++++++++++++++
>   4 files changed, 57 insertions(+)
> 

With the following nitpick addressed:

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

> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index 1ada23a6ec19..cce445ff8e3f 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -17,6 +17,7 @@
>   #include <asm/early_ioremap.h>
>   #include <asm/alternative.h>
>   #include <asm/cpufeature.h>
> +#include <asm/rsi.h>
>   
>   /*
>    * Generic IO read/write.  These perform native-endian accesses.
> @@ -318,4 +319,11 @@ extern bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
>   					unsigned long flags);
>   #define arch_memremap_can_ram_remap arch_memremap_can_ram_remap
>   
> +static inline bool arm64_is_mmio_private(phys_addr_t phys_addr, size_t size)
> +{
> +	if (unlikely(is_realm_world()))
> +		return arm64_is_protected_mmio(phys_addr, size);
> +	return false;
> +}
> +

The function names (arm64_is_{mmio_private, protected_mmio} are indicators to the
MMIO region's state or property. arm64_is_mmio_private() indicates the MMIO region
is 'private MMIO' while arm64_is_protected_mmio() indicates the MMIO region is
'protected MMIO'. They are equivalent and it may be worthy to unify the function
names (indicators) as below.

   option#1                         option#2
   --------                         --------
   arm64_is_private_mmio            arm64_is_protected_mmio
   __arm64_is_private_mmio          __arm64_is_protected_mmio


>   #endif	/* __ASM_IO_H */
> diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
> index acba065eb00e..42ff93c7b0ba 100644
> --- a/arch/arm64/include/asm/rsi.h
> +++ b/arch/arm64/include/asm/rsi.h
> @@ -14,6 +14,8 @@ DECLARE_STATIC_KEY_FALSE(rsi_present);
>   
>   void __init arm64_rsi_init(void);
>   
> +bool arm64_is_protected_mmio(phys_addr_t base, size_t size);
> +
>   static inline bool is_realm_world(void)
>   {
>   	return static_branch_unlikely(&rsi_present);
> diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
> index b661331c9204..fdb47f690307 100644
> --- a/arch/arm64/include/asm/rsi_cmds.h
> +++ b/arch/arm64/include/asm/rsi_cmds.h
> @@ -45,6 +45,27 @@ static inline unsigned long rsi_get_realm_config(struct realm_config *cfg)
>   	return res.a0;
>   }
>   
> +static inline unsigned long rsi_ipa_state_get(phys_addr_t start,
> +					      phys_addr_t end,
> +					      enum ripas *state,
> +					      phys_addr_t *top)
> +{
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_smc(SMC_RSI_IPA_STATE_GET,
> +		      start, end, 0, 0, 0, 0, 0,
> +		      &res);
> +
> +	if (res.a0 == RSI_SUCCESS) {
> +		if (top)
> +			*top = res.a1;
> +		if (state)
> +			*state = res.a2;
> +	}
> +
> +	return res.a0;
> +}
> +
>   static inline unsigned long rsi_set_addr_range_state(phys_addr_t start,
>   						     phys_addr_t end,
>   						     enum ripas state,
> diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> index a6495a64d9bb..d7bba4cee627 100644
> --- a/arch/arm64/kernel/rsi.c
> +++ b/arch/arm64/kernel/rsi.c
> @@ -66,6 +66,32 @@ static void __init arm64_rsi_setup_memory(void)
>   	}
>   }
>   
> +bool arm64_is_protected_mmio(phys_addr_t base, size_t size)
> +{
> +	enum ripas ripas;
> +	phys_addr_t end, top;
> +
> +	/* Overflow ? */
> +	if (WARN_ON(base + size <= base))
> +		return false;
> +
> +	end = ALIGN(base + size, RSI_GRANULE_SIZE);
> +	base = ALIGN_DOWN(base, RSI_GRANULE_SIZE);
> +
> +	while (base < end) {
> +		if (WARN_ON(rsi_ipa_state_get(base, end, &ripas, &top)))
> +			break;
> +		if (WARN_ON(top <= base))
> +			break;
> +		if (ripas != RSI_RIPAS_DEV)
> +			break;
> +		base = top;
> +	}
> +
> +	return base >= end;
> +}
> +EXPORT_SYMBOL(arm64_is_protected_mmio);
> +

The function may be worthy to be renamed to __arm64_is_private_mmio, as explained
as above.

>   void __init arm64_rsi_init(void)
>   {
>   	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)

Thanks,
Gavin