Re: [PATCH v15 05/14] x86/sgx: Implement basic EPC misc cgroup functionality

[Huang, Kai]

On Tue, 2024-06-18 at 07:56 -0500, Haitao Huang wrote:
> On Tue, 18 Jun 2024 06:31:09 -0500, Huang, Kai <kai.huang@xxxxxxxxx> wrote:
> 
> > 
> > > @@ -921,7 +956,8 @@ static int __init sgx_init(void)
> > >  	if (!sgx_page_cache_init())
> > >  		return -ENOMEM;
> > > 
> > > -	if (!sgx_page_reclaimer_init()) {
> > > +	if (!sgx_page_reclaimer_init() || !sgx_cgroup_init()) {
> > > +		misc_cg_set_capacity(MISC_CG_RES_SGX_EPC, 0);
> > >  		ret = -ENOMEM;
> > >  		goto err_page_cache;
> > >  	}
> > 
> > This code change is wrong due to two reasons:
> > 
> > 1) If sgx_page_reclaimer_init() was successful, but sgx_cgroup_init()
> > failed, you actually need to 'goto err_kthread' because the ksgxd()  
> > kernel
> > thread is already created and is running.
> > 
> > 2) There are other cases after here that can also result in sgx_init() to
> > fail completely, e.g., registering sgx_dev_provision mics device.  We  
> > need
> > to reset the capacity to 0 for those cases as well.
> > 
> > AFAICT, you need something like:
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c
> > b/arch/x86/kernel/cpu/sgx/main.c
> > index 27892e57c4ef..46f9c26992a7 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -930,6 +930,10 @@ static int __init sgx_init(void)
> >         if (ret)
> >                 goto err_kthread;
> > +       ret = sgx_cgroup_init();
> > +       if (ret)
> > +               goto err_provision;
> > +
> >         /*
> >          * Always try to initialize the native *and* KVM drivers.
> >          * The KVM driver is less picky than the native one and
> > @@ -941,10 +945,12 @@ static int __init sgx_init(void)
> >         ret = sgx_drv_init();
> >        if (sgx_vepc_init() && ret)
> > -               goto err_provision;
> > +               goto err_cgroup;
> >        return 0;
> > +err_cgroup:
> > +       /* SGX EPC cgroup cleanup */
> >  err_provision:
> >         misc_deregister(&sgx_dev_provision);
> > @@ -952,6 +958,8 @@ static int __init sgx_init(void)
> >         kthread_stop(ksgxd_tsk);
> > err_page_cache:
> > +       misc_misc_cg_set_capacity(MISC_CG_RES_SGX_EPC, 0);
> > +
> >         for (i = 0; i < sgx_nr_epc_sections; i++) {
> >                 vfree(sgx_epc_sections[i].pages);
> >                 memunmap(sgx_epc_sections[i].virt_addr);
> > 
> > 
> > I put the sgx_cgroup_init() before sgx_drv_init() and sgx_vepc_init(),
> > otherwise you will need sgx_drv_cleanup() and sgx_vepc_cleanup()
> > respectively when sgx_cgroup_init() fails.
> > 
> 
> Yes, good catch.
> 
> > This looks a little bit weird too, though:
> > 
> > Calling misc_misc_cg_set_capacity() to reset capacity to 0 is done at end
> > of sgx_init() error path, because the "set capacity" part is done in
> > sgx_epc_cache_init().  
> > But logically, both "set capacity" and "reset capacity to 0" should be  
> > SGX
> > EPC cgroup operation, so it's more reasonable to do "set capacity" in
> > sgx_cgroup_init() and do "reset to 0" in the
> > 
> > 	/* SGX EPC cgroup cleanup */
> > 
> > as shown above.
> > 
> > Eventually, you will need to do EPC cgroup cleanup anyway, e.g., to free
> > the workqueue, so it's odd to have two places to handle EPC cgroup
> > cleanup.
> > 
> > I understand the reason "set capacity" part is done in
> > sgx_page_cache_init() now is because in that function you can easily get
> > the capacity.  But the fact is @sgx_numa_nodes also tracks EPC size for
> > each node, so you can also get the total EPC size from @sgx_numa_node in
> > sgx_cgroup_init() and set capacity there.
> > 
> > In this case, you can put "reset capacity to 0" and "free workqueue"
> > together as the "SGX EPC cgroup cleanup", which is way more clear IMHO.
> > 
> Okay, will  expose @sgx_numa_nodes to epc_cgroup.c and do the calculations  
> in sgx_cgroup_init().
> 

Looks you will also need to expose @sgx_numa_mask, which looks overkill.

Other options:

1) Expose a function to return total EPC pages/size in "sgx.h".

2) Move out the new 'capacity' variable in this patch as a global variable
and expose it in "sgx.h" (perhaps rename to 'sgx_total_epc_pages/size').

3) Make sgx_cgroup_init() to take an argument of total EPC pages/size, and
pass it in sgx_init().  

For 3) there are also options to get total EPC pages/size:

a) Move out the new 'capacity' variable in this patch as a static.

b) Add a function to calculate total EPC pages/size from sgx_numa_nodes.

Hmm.. I think we can just use option 2)?