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SubjectRe: [PATCH v3 2/2] firmware: arm_scmi: Augment SMC/HVC to allow optional parameter
From
On 4/17/23 10:44, Nikunj Kela wrote:
> This patch add support for passing shmem channel address as parameter
> in smc/hvc call. This patch is useful when multiple scmi instances are
> using same smc-id and firmware needs to distiguish among the instances.

Typo: distinguish.

It really would have been a lot clearer and made a whole lot more sense
to encode a VM ID/channel number within some of the SMCCC parameters,
possibly as part of the function ID itself.

>
> Signed-off-by: Nikunj Kela <quic_nkela@quicinc.com>
> ---
> drivers/firmware/arm_scmi/driver.c | 1 +
> drivers/firmware/arm_scmi/smc.c | 25 ++++++++++++++++++++++++-
> 2 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index e7d97b59963b..b5957cc12fee 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -2914,6 +2914,7 @@ static const struct of_device_id scmi_of_match[] = {
> #endif
> #ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
> { .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> + { .compatible = "arm,scmi-smc-param", .data = &scmi_smc_desc},
> #endif
> #ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
> { .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
> diff --git a/drivers/firmware/arm_scmi/smc.c b/drivers/firmware/arm_scmi/smc.c
> index 93272e4bbd12..e28387346d33 100644
> --- a/drivers/firmware/arm_scmi/smc.c
> +++ b/drivers/firmware/arm_scmi/smc.c
> @@ -20,6 +20,9 @@
>
> #include "common.h"
>
> +#define lower32(x) ((u32)((x) & 0xffffffff))
> +#define upper32(x) ((u32)(((u64)(x) >> 32) & 0xffffffff))

Cannot you use the existing lower_32_bits and upper_32_bits macros from
kernel.h here?

> +
> /**
> * struct scmi_smc - Structure representing a SCMI smc transport
> *
> @@ -30,6 +33,8 @@
> * @inflight: Atomic flag to protect access to Tx/Rx shared memory area.
> * Used when operating in atomic mode.
> * @func_id: smc/hvc call function id
> + * @is_smc64: smc/hvc calling convention type 64 vs 32
> + * @param: physical address of the shmem channel
> */
>
> struct scmi_smc {
> @@ -40,6 +45,8 @@ struct scmi_smc {
> #define INFLIGHT_NONE MSG_TOKEN_MAX
> atomic_t inflight;
> u32 func_id;
> + bool is_smc64;
> + phys_addr_t param;
> };
>
> static irqreturn_t smc_msg_done_isr(int irq, void *data)
> @@ -137,6 +144,8 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> if (ret < 0)
> return ret;
>
> + if (of_device_is_compatible(dev->of_node, "arm,scmi-smc-param"))
> + scmi_info->param = res.start;

There is not even a check that this is going to be part of the kernel's
view of memory, that seems a bit brittle and possibly a security hole,
too. Your hypervisor presumably needs to have carved out some amount of
memory in order for the messages to be written to/read from, and so
would the VM kernel, so eventually we should have a 'reserved-memory'
entry of some sort, no?

> /*
> * If there is an interrupt named "a2p", then the service and
> * completion of a message is signaled by an interrupt rather than by
> @@ -156,6 +165,7 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> }
>
> scmi_info->func_id = func_id;
> + scmi_info->is_smc64 = ARM_SMCCC_IS_64(func_id);
> scmi_info->cinfo = cinfo;
> smc_channel_lock_init(scmi_info);
> cinfo->transport_info = scmi_info;
> @@ -188,7 +198,20 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
>
> shmem_tx_prepare(scmi_info->shmem, xfer, cinfo);
>
> - arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
> +#ifdef CONFIG_ARM64
> + /*
> + * if SMC32 convention is used, pass 64 bit address in
> + * two parameters
> + */
> + if (!scmi_info->is_smc64)

There is no need for scmi_info to store is_smc64, just check the func_id
here and declare is_smc64 as a local variable to the function.

Also, another way to approach this would be to encode the parameters
region in 4KB units such that event on a 32-bit system with LPAE you are
guaranteed to fit the region into a 32-bit unsigned long. AFAIR
virtualization and LPAE are indistinguishable on real CPUs?

> + arm_smccc_1_1_invoke(scmi_info->func_id,
> + lower32(scmi_info->param),
> + upper32(scmi_info->param),
> + 0, 0, 0, 0, 0, &res);
> + else
> +#endif
> + arm_smccc_1_1_invoke(scmi_info->func_id, scmi_info->param,
> + 0, 0, 0, 0, 0, 0, &res);
>
> /* Only SMCCC_RET_NOT_SUPPORTED is valid error code */
> if (res.a0) {

--
Florian

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