On 2022/4/19 上午2:14, Jacob Pan wrote:
Hi [email protected],
On Sat, 16 Apr 2022 09:43:07 +0800, "[email protected]"
<[email protected]> wrote:
On 2022/4/16 上午5:00, Jacob Pan wrote:
Hi [email protected],
On Fri, 15 Apr 2022 19:52:03 +0800, "[email protected]"
<[email protected]> 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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