Re: [PATCH v4 4/6] remoteproc: qcom: pas: Map/unmap subsystem region before auth_and_reset

On Fri, May 01, 2026 at 12:42:51AM +0530, Mukesh Ojha wrote:
> Qualcomm remoteproc drivers such as qcom_q6v5_mss, which do not use the
> Peripheral Authentication Service (PAS), always map the MBA region before
> use and unmap it once the usage is complete. This behavior was introduced
> to avoid issues seen in the past where speculative accesses from the
> application processor to the MBA region after it was assigned to the remote
> Q6 led to an XPU violation. The issue was mitigated by unmapping the region
> before handing control to the remote Q6.
> 
> Currently, most Qualcomm SoCs using the PAS driver run either with a
> standalone QHEE or the Gunyah hypervisor. In these environments, the
> hypervisor unmaps the Q6 memory from HLOS Stage-2 and remaps it into the
> Q6 Stage-2 page table. As a result, speculative accesses from HLOS cannot
> reach the region even if it remains mapped in HLOS Stage-1; therefore, XPU
> violations cannot occur.
> 
> However, when the same SoC runs Linux at EL2, Linux itself must perform the
> unmapping to avoid such issues. It is still correct to apply this mapping/
> unmapping sequence even for SoCs that run under Gunyah, so this behavior
> should not be conditional.
> 
> Signed-off-by: Mukesh Ojha <[email protected]>
> ---
>  drivers/remoteproc/qcom_q6v5_pas.c  | 45 ++++++++++++++++++++---------
>  drivers/soc/qcom/mdt_loader.c       | 18 +++++++++---
>  include/linux/soc/qcom/mdt_loader.h |  4 +--
>  3 files changed, 48 insertions(+), 19 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <[email protected]>


-- 
With best wishes
Dmitry