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    Subject[PATCH v2 06/18] x86/sgx: Introduce RECLAIM_IN_PROGRESS flag for EPC pages
    Date
    From: Sean Christopherson <sean.j.christopherson@intel.com>

    When selecting pages to be reclaimed from the page pool (sgx_global_lru),
    the list of reclaimable pages is walked, and any page that is both
    reclaimable and not in the process of being freed is added to a list of
    potential candidates to be reclaimed. After that, this separate list is
    further examined and may or may not ultimately be reclaimed. In order
    to prevent this page from being removed from the sgx_epc_lru_lists
    struct in a separate thread by sgx_drop_epc_page(), keep track of
    whether the EPC page is in the middle of being reclaimed with
    the addtion of a RECLAIM_IN_PROGRESS flag, and do not delete the page
    off the LRU in sgx_drop_epc_page() if it has not yet finished being
    reclaimed.

    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
    Cc: Sean Christopherson <seanjc@google.com>
    ---
    arch/x86/kernel/cpu/sgx/main.c | 15 ++++++++++-----
    arch/x86/kernel/cpu/sgx/sgx.h | 2 ++
    2 files changed, 12 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
    index ecd7f8e704cc..bad72498b0a7 100644
    --- a/arch/x86/kernel/cpu/sgx/main.c
    +++ b/arch/x86/kernel/cpu/sgx/main.c
    @@ -305,13 +305,15 @@ static void __sgx_reclaim_pages(void)

    encl_page = epc_page->encl_owner;

    - if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
    + if (kref_get_unless_zero(&encl_page->encl->refcount) != 0) {
    + epc_page->flags |= SGX_EPC_PAGE_RECLAIM_IN_PROGRESS;
    chunk[cnt++] = epc_page;
    - else
    + } else {
    /* The owner is freeing the page. No need to add the
    * page back to the list of reclaimable pages.
    */
    epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
    + }
    }
    spin_unlock(&sgx_global_lru.lock);

    @@ -337,6 +339,7 @@ static void __sgx_reclaim_pages(void)

    skip:
    spin_lock(&sgx_global_lru.lock);
    + epc_page->flags &= ~SGX_EPC_PAGE_RECLAIM_IN_PROGRESS;
    sgx_epc_push_reclaimable(&sgx_global_lru, epc_page);
    spin_unlock(&sgx_global_lru.lock);

    @@ -360,7 +363,8 @@ static void __sgx_reclaim_pages(void)
    sgx_reclaimer_write(epc_page, &backing[i]);

    kref_put(&encl_page->encl->refcount, sgx_encl_release);
    - epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
    + epc_page->flags &= ~(SGX_EPC_PAGE_RECLAIMER_TRACKED |
    + SGX_EPC_PAGE_RECLAIM_IN_PROGRESS);

    sgx_free_epc_page(epc_page);
    }
    @@ -508,7 +512,8 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
    void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags)
    {
    spin_lock(&sgx_global_lru.lock);
    - WARN_ON(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
    + WARN_ON(page->flags & (SGX_EPC_PAGE_RECLAIMER_TRACKED |
    + SGX_EPC_PAGE_RECLAIM_IN_PROGRESS));
    page->flags |= flags;
    if (flags & SGX_EPC_PAGE_RECLAIMER_TRACKED)
    sgx_epc_push_reclaimable(&sgx_global_lru, page);
    @@ -532,7 +537,7 @@ int sgx_drop_epc_page(struct sgx_epc_page *page)
    spin_lock(&sgx_global_lru.lock);
    if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
    /* The page is being reclaimed. */
    - if (list_empty(&page->list)) {
    + if (page->flags & SGX_EPC_PAGE_RECLAIM_IN_PROGRESS) {
    spin_unlock(&sgx_global_lru.lock);
    return -EBUSY;
    }
    diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
    index ba4338b7303f..37d66bc6ca27 100644
    --- a/arch/x86/kernel/cpu/sgx/sgx.h
    +++ b/arch/x86/kernel/cpu/sgx/sgx.h
    @@ -30,6 +30,8 @@
    #define SGX_EPC_PAGE_IS_FREE BIT(1)
    /* Pages allocated for KVM guest */
    #define SGX_EPC_PAGE_KVM_GUEST BIT(2)
    +/* page flag to indicate reclaim is in progress */
    +#define SGX_EPC_PAGE_RECLAIM_IN_PROGRESS BIT(3)

    struct sgx_epc_page {
    unsigned int section;
    --
    2.38.1
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