Re: [PATCH v8 10/12] firmware: qcom: tzmem: enable SHM Bridge support

[Kuldeep Singh <quic_kuldsing@quicinc.com>]

On Sun, Mar 03, 2024 at 04:01:13PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> 
> SHM Bridge is a safety mechanism allowing to limit the amount of memory
> shared between the kernel and the TrustZone to regions explicitly marked
> as such.
> 
> Add a variant of the tzmem allocator that configures the memory pools as
> SHM bridges. It also enables the SHM bridge globally so non-SHM bridge
> memory will no longer work with SCM calls.
> 
> If enabled at build-time, it will still be checked for availability at
> run-time. If the architecture doesn't support SHM Bridge, the allocator
> will fall back to the generic mode.
> 
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> Tested-by: Andrew Halaney <ahalaney@redhat.com> # sc8280xp-lenovo-thinkpad-x13s
> Tested-by: Deepti Jaggi <quic_djaggi@quicinc.com> #sa8775p-ride
> Reviewed-by: Elliot Berman <quic_eberman@quicinc.com>
> ---
>  drivers/firmware/qcom/Kconfig      | 10 +++++
>  drivers/firmware/qcom/qcom_tzmem.c | 65 +++++++++++++++++++++++++++++-
>  2 files changed, 74 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/qcom/Kconfig b/drivers/firmware/qcom/Kconfig
> index 4634f8cecc7b..7f6eb4174734 100644
> --- a/drivers/firmware/qcom/Kconfig
> +++ b/drivers/firmware/qcom/Kconfig
> @@ -28,6 +28,16 @@ config QCOM_TZMEM_MODE_GENERIC
>  	  Use the generic allocator mode. The memory is page-aligned, non-cachable
>  	  and physically contiguous.
>  
> +config QCOM_TZMEM_MODE_SHMBRIDGE
> +	bool "SHM Bridge"
> +	help
> +	  Use Qualcomm Shared Memory Bridge. The memory has the same alignment as
> +	  in the 'Generic' allocator but is also explicitly marked as an SHM Bridge
> +	  buffer.
> +
> +	  With this selected, all buffers passed to the TrustZone must be allocated
> +	  using the TZMem allocator or else the TrustZone will refuse to use them.
> +
>  endchoice
>  
>  config QCOM_SCM_DOWNLOAD_MODE_DEFAULT
> diff --git a/drivers/firmware/qcom/qcom_tzmem.c b/drivers/firmware/qcom/qcom_tzmem.c
> index 23f364afa6ca..244615e8c505 100644
> --- a/drivers/firmware/qcom/qcom_tzmem.c
> +++ b/drivers/firmware/qcom/qcom_tzmem.c
> @@ -67,7 +67,70 @@ static void qcom_tzmem_cleanup_area(struct qcom_tzmem_area *area)
>  
>  }
>  
> -#endif /* CONFIG_QCOM_TZMEM_MODE_GENERIC */
> +#elif IS_ENABLED(CONFIG_QCOM_TZMEM_MODE_SHMBRIDGE)
> +
> +#include <linux/firmware/qcom/qcom_scm.h>
> +
> +#define QCOM_SHM_BRIDGE_NUM_VM_SHIFT 9
> +
> +static bool qcom_tzmem_using_shm_bridge;
> +
> +static int qcom_tzmem_init(void)
> +{
> +	int ret;
> +
> +	ret = qcom_scm_shm_bridge_enable();
> +	if (ret == -EOPNOTSUPP) {
> +		dev_info(qcom_tzmem_dev, "SHM Bridge not supported\n");
> +		return 0;
> +	}
> +
> +	if (!ret)
> +		qcom_tzmem_using_shm_bridge = true;
> +
> +	return ret;
> +}
> +
> +static int qcom_tzmem_init_area(struct qcom_tzmem_area *area)
> +{
> +	u64 pfn_and_ns_perm, ipfn_and_s_perm, size_and_flags, ns_perms;
> +	int ret;
> +
> +	if (!qcom_tzmem_using_shm_bridge)
> +		return 0;
> +
> +	ns_perms = (QCOM_SCM_PERM_WRITE | QCOM_SCM_PERM_READ);

Above expr can be replaced with QCOM_SCM_PERM_RW.
https://elixir.bootlin.com/linux/v6.8-rc7/source/include/linux/firmware/qcom/qcom_scm.h#L59

Regards
Kuldeep