On Thu, May 15, 2025 at 08:20:44AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen <nicol...@nvidia.com> > > Sent: Friday, May 9, 2025 11:03 AM > > > > To simplify the mappings from global VCMDQs to VINTFs' LVCMDQs, the > > design > > chose to do static allocations and mappings in the global reset function. > > > > However, with the user-owned VINTF support, it exposes a security concern: > > if user space VM only wants one LVCMDQ for a VINTF, statically mapping two > > or more LVCMDQs creates a hidden VCMDQ that user space could DoS attack > > by > > writing random stuff to overwhelm the kernel with unhandleable IRQs. > > > > Thus, to support the user-owned VINTF feature, a LVCMDQ mapping has to > > be > > done dynamically. > > > > HW allows pre-assigning global VCMDQs in the CMDQ_ALLOC registers, > > without > > finalizing the mappings by keeping CMDQV_CMDQ_ALLOCATED=0. So, add a > > pair > > of map/unmap helper that simply sets/clears that bit. > > > > Delay the LVCMDQ mappings to tegra241_vintf_hw_init(), and the > > unmappings > > to tegra241_vintf_hw_deinit(). > > I don't know the specifics of tegra241-cmdqv. But the current description > is a bit misleading. for native tegra241_vintf_hw_init() is called from reset > so the mapping is still enabled in that path. for user-owned then > tegra241_vcmdq_map_lvcmdq() is called from tegra241_vintf_alloc_lvcmdq_user() > instead of tegra241_vintf_hw_init(). > > so nothing is actually delayed in this patch.
It is delayed from tegra241_cmdqv_hw_reset() to later functions. The in-kernel VINTF0 is not literally delayed fundamentally as you mentioned because it needs to be allocated/mapped in probe(). The user-space VINTFs was previously allocated/mapped in probe(), now it's moved to user space handler, i.e. no mapping until user space asks for one. Perhaps I can make this "delay" statement more narrative for a clarification. Thanks Nicolin
