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

Haitao Huang
2024-02-23T18:46:45Z

On Thu, 22 Feb 2024 16:44:45 -0600, Huang, Kai <kai.huang@intel.com> wrote:

>
>
> 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.
>

Will do

Thanks
Haitao