Re: [PATCH v5 09/18] x86/sgx: Store struct sgx_encl when allocating new VA pages

Haitao Huang
2023-09-27T15:35:31Z

Hi Kai,

On Wed, 27 Sep 2023 06:14:20 -0500, Huang, Kai <kai.huang@intel.com> wrote:

> On Fri, 2023-09-22 at 20:06 -0700, Haitao Huang wrote:
>> From: Sean Christopherson <sean.j.christopherson@intel.com>
>>
>> In a later patch, when a cgroup has exceeded the max capacity for EPC
>> pages, it may need to identify and OOM kill a less active enclave to
>> make room for other enclaves within the same group. Such a victim
>> enclave would have no active pages other than the unreclaimable Version
>> Array (VA) and SECS pages. Therefore, the cgroup needs examine its
>> unreclaimable page list, and finding an enclave given a SECS page or a
>> VA page. This will require a backpointer from a page to an enclave,
>> which is not available for VA pages.
>>
>> Because struct sgx_epc_page instances of VA pages are not owned by an
>> sgx_encl_page instance, mark their owner as sgx_encl: pass the struct
>> sgx_encl of the enclave allocating the VA page to sgx_alloc_epc_page(),
>> which will store this value in the owner field of the struct
>> sgx_epc_page. In a later patch, VA pages will be placed in an
>> unreclaimable queue that can be examined by the cgroup to select the OOM
>> killed enclave.
>>
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>> Co-developed-by: Kristen Carlson Accardi <kristen@linux.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>
>> Cc: Sean Christopherson <seanjc@google.com>
>>
>
> [...]
>
>> @@ -562,7 +562,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void
>> *owner, bool reclaim)
>> for ( ; ; ) {
>> page = __sgx_alloc_epc_page();
>> if (!IS_ERR(page)) {
>> - page->owner = owner;
>> + page->encl_page = owner;
>
> Looks using 'encl_page' is arbitrary.
>
> Also actually for virtual EPC page the owner is set to the 'sgx_vepc'
> instance.
>
>> break;
>> }
>>
>> @@ -607,7 +607,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
>>
>> spin_lock(&node->lock);
>>
>> - page->owner = NULL;
>> + page->encl_page = NULL;
>
> Ditto.
>
>> if (page->poison)
>> list_add(&page->list, &node->sgx_poison_page_list);
>> else
>> @@ -642,7 +642,7 @@ static bool __init sgx_setup_epc_section(u64
>> phys_addr, u64 size,
>> for (i = 0; i < nr_pages; i++) {
>> section->pages[i].section = index;
>> section->pages[i].flags = 0;
>> - section->pages[i].owner = NULL;
>> + section->pages[i].encl_page = NULL;
>> section->pages[i].poison = 0;
>> list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
>> }
>> diff --git a/arch/x86/kernel/cpu/sgx/sgx.h
>> b/arch/x86/kernel/cpu/sgx/sgx.h
>> index 764cec23f4e5..5110dd433b80 100644
>> --- a/arch/x86/kernel/cpu/sgx/sgx.h
>> +++ b/arch/x86/kernel/cpu/sgx/sgx.h
>> @@ -68,7 +68,12 @@ struct sgx_epc_page {
>> unsigned int section;
>> u16 flags;
>> u16 poison;
>> - struct sgx_encl_page *owner;
>> +
>> + /* Possible owner types */
>> + union {
>> + struct sgx_encl_page *encl_page;
>> + struct sgx_encl *encl;
>> + };
>
> Sadly for virtual EPC page the owner is set to the 'sgx_vepc' instance it
> belongs to.
>
> Given how sgx_{alloc|free}_epc_page() arbitrarily uses encl_page,
> perhaps we
> should do below?
>
> union {
> struct sgx_encl_page *encl_page;
> struct sgx_encl *encl;
> struct sgx_vepc *vepc;
> void *owner;
> };
>
> And in sgx_{alloc|free}_epc_page() we can use 'owner' instead.
>

As I mentioned in cover letter and change log in 11/18, this series does
not track virtual EPC.
We can add vepc field into the union in future if such tracking is needed.
Don't think "void *owner" is needed though.

Thanks
Haitao