Messages in this thread | | | Subject | Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit | From | "" <> | Date | Tue, 19 Apr 2022 09:02:52 +0800 |
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On 2022/4/19 上午2:14, Jacob Pan wrote: > Hi zhangfei.gao@foxmail.com, > > On Sat, 16 Apr 2022 09:43:07 +0800, "zhangfei.gao@foxmail.com" > <zhangfei.gao@foxmail.com> wrote: > >> On 2022/4/16 上午5:00, Jacob Pan wrote: >>> Hi zhangfei.gao@foxmail.com, >>> >>> On Fri, 15 Apr 2022 19:52:03 +0800, "zhangfei.gao@foxmail.com" >>> <zhangfei.gao@foxmail.com> wrote: >>> >>>>>>> A PASID might be still used even though it is freed on mm exit. >>>>>>> >>>>>>> process A: >>>>>>> sva_bind(); >>>>>>> ioasid_alloc() = N; // Get PASID N for the mm >>>>>>> fork(): // spawn process B >>>>>>> exit(); >>>>>>> ioasid_free(N); >>>>>>> >>>>>>> process B: >>>>>>> device uses PASID N -> failure >>>>>>> sva_unbind(); >>>>>>> >>>>>>> Dave Hansen suggests to take a refcount on the mm whenever binding >>>>>>> the PASID to a device and drop the refcount on unbinding. The mm >>>>>>> won't be dropped if the PASID is still bound to it. >>>>>>> >>>>>>> Fixes: 701fac40384f ("iommu/sva: Assign a PASID to mm on PASID >>>>>>> allocation and free it on mm exit") >>>>>>> >>> Is process A's mm intended to be used by process B? Or you really should >>> use PASID N on process B's mm? If the latter, it may work for a while >>> until B changes mapping. >>> >>> It seems you are just extending the life of a defunct mm? >> From nginx code, the master process init resources, then fork daemon >> process to take over, >> then master process exit by itself. >> >> src/core/nginx.c >> main >> ngx_ssl_init(log); -> openssl engine -> bind_fn -> sva_bind() >> ngx_daemon(cycle->log) >> >> src/os/unix/ngx_daemon.c >> ngx_daemon(ngx_log_t *log) >> { >> int fd; >> >> switch (fork()) { >> case -1: >> ngx_log_error(NGX_LOG_EMERG, log, ngx_errno, "fork() failed"); >> return NGX_ERROR; >> >> case 0: >> // the fork daemon process >> break; >> > Does this child process call sva_bind() again to get another PASID? Or it > will keep using the parent's PASID for DMA? The master process call sva_bind (PASID A), fork daemon process, then exit.
The daemon process does not call sva_bind again, only for managing worker processes.
The worker process will call sva_bind for new PASID (B), for real transaction.
The worker process will free the PASID (B) when worker process exit like nginx quit.
nginx -s quit does not free PASID A via callback, which may should be freed by signal handler in engine itself, still in check.
Thanks
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