Subject: Re: [PATCH v10 03/43] arm64: RME: Add SMC definitions for calling the RMM

From: Marc Zyngier <[email-masked]>
Date: Wed, 01 Oct 2025 11:05:00 +0100

On Wed, 20 Aug 2025 15:55:23 +0100,
Steven Price <[email-masked]> wrote:
> 
> The RMM (Realm Management Monitor) provides functionality that can be
> accessed by SMC calls from the host.
> 
> The SMC definitions are based on DEN0137[1] version 1.0-rel0
> 
> [1] https://developer.arm.com/documentation/den0137/1-0rel0/
> 
> Reviewed-by: Gavin Shan <[email-masked]>
> Reviewed-by: Suzuki K Poulose <[email-masked]>
> Signed-off-by: Steven Price <[email-masked]>
> ---
> Changes since v9:
>  * Corrected size of 'ripas_value' in struct rec_exit. The spec states
>    this is an 8-bit type with padding afterwards (rather than a u64).
> Changes since v8:
>  * Added RMI_PERMITTED_GICV3_HCR_BITS to define which bits the RMM
>    permits to be modified.
> Changes since v6:
>  * Renamed REC_ENTER_xxx defines to include 'FLAG' to make it obvious
>    these are flag values.
> Changes since v5:
>  * Sorted the SMC #defines by value.
>  * Renamed SMI_RxI_CALL to SMI_RMI_CALL since the macro is only used for
>    RMI calls.
>  * Renamed REC_GIC_NUM_LRS to REC_MAX_GIC_NUM_LRS since the actual
>    number of available list registers could be lower.
>  * Provided a define for the reserved fields of FeatureRegister0.
>  * Fix inconsistent names for padding fields.
> Changes since v4:
>  * Update to point to final released RMM spec.
>  * Minor rearrangements.
> Changes since v3:
>  * Update to match RMM spec v1.0-rel0-rc1.
> Changes since v2:
>  * Fix specification link.
>  * Rename rec_entry->rec_enter to match spec.
>  * Fix size of pmu_ovf_status to match spec.
> ---
>  arch/arm64/include/asm/rmi_smc.h | 269 +++++++++++++++++++++++++++++++
>  1 file changed, 269 insertions(+)
>  create mode 100644 arch/arm64/include/asm/rmi_smc.h
> 
> diff --git a/arch/arm64/include/asm/rmi_smc.h b/arch/arm64/include/asm/rmi_smc.h
> new file mode 100644
> index 000000000000..1000368f1bca
> --- /dev/null
> +++ b/arch/arm64/include/asm/rmi_smc.h

[...]

> +#define RMI_PERMITTED_GICV3_HCR_BITS	(ICH_HCR_EL2_UIE |		\
> +					 ICH_HCR_EL2_LRENPIE |		\
> +					 ICH_HCR_EL2_NPIE |		\
> +					 ICH_HCR_EL2_VGrp0EIE |		\
> +					 ICH_HCR_EL2_VGrp0DIE |		\
> +					 ICH_HCR_EL2_VGrp1EIE |		\
> +					 ICH_HCR_EL2_VGrp1DIE |		\
> +					 ICH_HCR_EL2_TDIR)

Why should KVM care about what bits the RMM wants to use? Also, why
should KVM be forbidden to use the TALL0, TALL1 and TC bits? If
interrupt delivery is the host's business, then the RMM has no
business interfering with the GIC programming.

> +
> +struct rec_enter {
> +	union { /* 0x000 */
> +		u64 flags;
> +		u8 padding0[0x200];
> +	};
> +	union { /* 0x200 */
> +		u64 gprs[REC_RUN_GPRS];
> +		u8 padding1[0x100];
> +	};
> +	union { /* 0x300 */
> +		struct {
> +			u64 gicv3_hcr;
> +			u64 gicv3_lrs[REC_MAX_GIC_NUM_LRS];
> +		};
> +		u8 padding2[0x100];
> +	};
> +	u8 padding3[0x400];
> +};
> +
> +#define RMI_EXIT_SYNC			0x00
> +#define RMI_EXIT_IRQ			0x01
> +#define RMI_EXIT_FIQ			0x02
> +#define RMI_EXIT_PSCI			0x03
> +#define RMI_EXIT_RIPAS_CHANGE		0x04
> +#define RMI_EXIT_HOST_CALL		0x05
> +#define RMI_EXIT_SERROR			0x06
> +
> +struct rec_exit {
> +	union { /* 0x000 */
> +		u8 exit_reason;
> +		u8 padding0[0x100];
> +	};
> +	union { /* 0x100 */
> +		struct {
> +			u64 esr;
> +			u64 far;
> +			u64 hpfar;
> +		};
> +		u8 padding1[0x100];
> +	};
> +	union { /* 0x200 */
> +		u64 gprs[REC_RUN_GPRS];
> +		u8 padding2[0x100];
> +	};
> +	union { /* 0x300 */
> +		struct {
> +			u64 gicv3_hcr;
> +			u64 gicv3_lrs[REC_MAX_GIC_NUM_LRS];
> +			u64 gicv3_misr;

Why do we care about ICH_MISR_EL2? Surely we get everything in the
registers themselves, right? I think this goes back to my question
above: why is the RMM getting in the way of ICH_*_EL2 accesses?

> +			u64 gicv3_vmcr;
> +		};

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.