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    SubjectRe: [PATCH v5 07/18] x86/sgx: Introduce RECLAIM_IN_PROGRESS state
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    On Sat Sep 23, 2023 at 6:06 AM EEST, Haitao Huang wrote:
    > From: Sean Christopherson <sean.j.christopherson@intel.com>
    >
    > Add RECLAIM_IN_PROGRESS state to not rely on list_empty(&epc_page->list)
    > to determine if an EPC page is selected as a reclaiming candidate.
    >
    > When a page is being reclaimed from the page pool (sgx_global_lru),
    > there is an intermediate stage where a page may have been identified as
    > a candidate for reclaiming, but has not yet been reclaimed. Currently
    > such pages are list_del_init()'d from the global LRU list, and stored in
    > a an array on stack. To prevent another thread from dropping the same
    > page in the middle of reclaiming, sgx_drop_epc_page() checks for
    > list_empty(&epc_page->list).
    >
    > A later patch will replace the array on stack with a temporary list to
    > store the candidate pages, so list_empty() should no longer be used for
    > this purpose.
    >
    > 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>
    > ---
    > V4:
    > - Fixed some typos.
    > - Revised commit message.
    >
    > V3:
    > - Extend the sgx_epc_page_state enum introduced earlier to replace the
    > flag based approach.
    > ---
    > arch/x86/kernel/cpu/sgx/main.c | 21 ++++++++++-----------
    > arch/x86/kernel/cpu/sgx/sgx.h | 16 ++++++++++++++++
    > 2 files changed, 26 insertions(+), 11 deletions(-)
    >
    > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
    > index b26860399402..c1ae19a154d0 100644
    > --- a/arch/x86/kernel/cpu/sgx/main.c
    > +++ b/arch/x86/kernel/cpu/sgx/main.c
    > @@ -312,13 +312,15 @@ static void sgx_reclaim_pages(void)
    > list_del_init(&epc_page->list);
    > encl_page = epc_page->owner;
    >
    > - if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
    > + if (kref_get_unless_zero(&encl_page->encl->refcount) != 0) {
    > + sgx_epc_page_set_state(epc_page, 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.
    > */
    > sgx_epc_page_reset_state(epc_page);
    > + }
    > }
    > spin_unlock(&sgx_global_lru.lock);
    >
    > @@ -528,16 +530,13 @@ void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags)
    > int sgx_drop_epc_page(struct sgx_epc_page *page)
    > {
    > spin_lock(&sgx_global_lru.lock);
    > - if (sgx_epc_page_reclaimable(page->flags)) {
    > - /* The page is being reclaimed. */
    > - if (list_empty(&page->list)) {
    > - spin_unlock(&sgx_global_lru.lock);
    > - return -EBUSY;
    > - }
    > -
    > - list_del(&page->list);
    > - sgx_epc_page_reset_state(page);
    > + if (sgx_epc_page_reclaim_in_progress(page->flags)) {
    > + spin_unlock(&sgx_global_lru.lock);
    > + return -EBUSY;
    > }
    > +
    > + list_del(&page->list);
    > + sgx_epc_page_reset_state(page);
    > spin_unlock(&sgx_global_lru.lock);
    >
    > return 0;
    > diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
    > index 2faeb40b345f..764cec23f4e5 100644
    > --- a/arch/x86/kernel/cpu/sgx/sgx.h
    > +++ b/arch/x86/kernel/cpu/sgx/sgx.h
    > @@ -40,6 +40,8 @@ enum sgx_epc_page_state {
    >
    > /* Page is in use and tracked in a reclaimable LRU list
    > * Becomes NOT_TRACKED after sgx_drop_epc()
    > + * Becomes RECLAIM_IN_PROGRESS in sgx_reclaim_pages() when identified
    > + * for reclaiming
    > */
    > SGX_EPC_PAGE_RECLAIMABLE = 2,
    >
    > @@ -50,6 +52,14 @@ enum sgx_epc_page_state {
    > */
    > SGX_EPC_PAGE_UNRECLAIMABLE = 3,
    >
    > + /* Page is being prepared for reclamation, tracked in a temporary
    > + * isolated list by the reclaimer.
    > + * Changes in sgx_reclaim_pages() back to RECLAIMABLE if preparation
    > + * fails for any reason.
    > + * Becomes NOT_TRACKED if reclaimed successfully in sgx_reclaim_pages()
    > + * and immediately sgx_free_epc() is called to make it FREE.
    > + */
    > + SGX_EPC_PAGE_RECLAIM_IN_PROGRESS = 4,
    > };
    >
    > #define SGX_EPC_PAGE_STATE_MASK GENMASK(2, 0)
    > @@ -73,6 +83,12 @@ static inline void sgx_epc_page_set_state(struct sgx_epc_page *page, unsigned lo
    > page->flags |= (flags & SGX_EPC_PAGE_STATE_MASK);
    > }
    >
    > +static inline bool sgx_epc_page_reclaim_in_progress(unsigned long flags)
    > +{
    > + return SGX_EPC_PAGE_RECLAIM_IN_PROGRESS == (flags &
    > + SGX_EPC_PAGE_STATE_MASK);
    > +}

    return SGX_EPC_PAGE_RECLAIM_IN_PROGRESS == (flags & SGX_EPC_PAGE_STATE_MASK);

    > +
    > static inline bool sgx_epc_page_reclaimable(unsigned long flags)
    > {
    > return SGX_EPC_PAGE_RECLAIMABLE == (flags & SGX_EPC_PAGE_STATE_MASK);
    > --
    > 2.25.1


    BR, Jarkko

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