Re: [PATCH v9 13/15] x86/sgx: Turn on per-cgroup EPC reclamation

["Huang, Kai" <kai.huang@intel.com>]

On 23/02/2024 5:36 am, Haitao Huang wrote:
> On Wed, 21 Feb 2024 05:23:00 -0600, Huang, Kai <kai.huang@intel.com> wrote:
> 
>> On Mon, 2024-02-05 at 13:06 -0800, Haitao Huang wrote:
>>> From: Kristen Carlson Accardi <kristen@linux.intel.com>
>>>
>>> Previous patches have implemented all infrastructure needed for
>>> per-cgroup EPC page tracking and reclaiming. But all reclaimable EPC
>>> pages are still tracked in the global LRU as sgx_lru_list() returns hard
>>> coded reference to the global LRU.
>>>
>>> Change sgx_lru_list() to return the LRU of the cgroup in which the given
>>> EPC page is allocated.
>>>
>>> This makes all EPC pages tracked in per-cgroup LRUs and the global
>>> reclaimer (ksgxd) will not be able to reclaim any pages from the global
>>> LRU. However, in cases of over-committing, i.e., sum of cgroup limits
>>> greater than the total capacity, cgroups may never reclaim but the total
>>> usage can still be near the capacity. Therefore global reclamation is
>>> still needed in those cases and it should reclaim from the root cgroup.
>>>
>>> Modify sgx_reclaim_pages_global(), to reclaim from the root EPC cgroup
>>> when cgroup is enabled, otherwise from the global LRU.
>>>
>>> Similarly, modify sgx_can_reclaim(), to check emptiness of LRUs of all
>>> cgroups when EPC cgroup is enabled, otherwise only check the global LRU.
>>>
>>> With these changes, the global reclamation and per-cgroup reclamation
>>> both work properly with all pages tracked in per-cgroup LRUs.
>>>
>>> Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
>>> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>>> Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
>>> Co-developed-by: Haitao Huang <haitao.huang@linux.intel.com>
>>> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
>>> ---
>>> V7:
>>> - Split this out from the big patch, #10 in V6. (Dave, Kai)
>>> ---
>>>  arch/x86/kernel/cpu/sgx/main.c | 16 +++++++++++++++-
>>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/kernel/cpu/sgx/main.c 
>>> b/arch/x86/kernel/cpu/sgx/main.c
>>> index 6b0c26cac621..d4265a390ba9 100644
>>> --- a/arch/x86/kernel/cpu/sgx/main.c
>>> +++ b/arch/x86/kernel/cpu/sgx/main.c
>>> @@ -34,12 +34,23 @@ static struct sgx_epc_lru_list sgx_global_lru;
>>>
>>>  static inline struct sgx_epc_lru_list *sgx_lru_list(struct 
>>> sgx_epc_page *epc_page)
>>>  {
>>> +#ifdef CONFIG_CGROUP_SGX_EPC
>>> +    if (epc_page->epc_cg)
>>> +        return &epc_page->epc_cg->lru;
>>> +
>>> +    /* This should not happen if kernel is configured correctly */
>>> +    WARN_ON_ONCE(1);
>>> +#endif
>>>      return &sgx_global_lru;
>>>  }
>>
>> How about when EPC cgroup is enabled, but one enclave doesn't belong 
>> to any EPC
>> cgroup?  Is it OK to track EPC pages for these enclaves to the root 
>> EPC cgroup's
>> LRU list together with other enclaves belongs to the root cgroup?
>>
>>
>> This should be a valid case, right?
> 
> There is no such case. Each page is in the root by default.
> 

Is it guaranteed by the (misc) cgroup design/implementation?  If so 
please add this information to the changelog and/or comments?  It helps 
non-cgroup expert like me to understand.