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Message-ID: <b1c1fe128ea6b012a3092d1150a2bf8a6773e36b.camel@linux.intel.com>
Date: Thu, 29 Sep 2022 16:04:14 -0700
From: Kristen Carlson Accardi <kristen@...ux.intel.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
cgroups@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH 04/20] x86/sgx: Add 'struct sgx_epc_lru' to
encapsulate lru list(s)
On Fri, 2022-09-23 at 16:20 +0300, Jarkko Sakkinen wrote:
> On Thu, Sep 22, 2022 at 10:10:41AM -0700, Kristen Carlson Accardi
> wrote:
> > From: Sean Christopherson <sean.j.christopherson@...el.com>
> >
> > Wrap the existing reclaimable list and its spinlock in a struct to
> > minimize the code changes needed to handle multiple LRUs as well as
> > reclaimable and non-reclaimable lists, both of which will be
> > introduced
> > and used by SGX EPC cgroups.
> >
> > Signed-off-by: Sean Christopherson
> > <sean.j.christopherson@...el.com>
> > Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> > Cc: Sean Christopherson <seanjc@...gle.com>
>
> The commit message could explicitly state the added data type.
>
> The data type is not LRU: together with the LIFO list, i.e.
> a queue, the code implements LRU alike policy.
>
> I would name the data type as sgx_epc_queue because it is a
> less confusing name.
I think when you look at patch 05/20 which adds the unreclaimable field
this becomes less like a straight up queue data type.
>
> > ---
> > arch/x86/kernel/cpu/sgx/main.c | 37 +++++++++++++++++-------------
> > ----
> > arch/x86/kernel/cpu/sgx/sgx.h | 11 ++++++++++
> > 2 files changed, 30 insertions(+), 18 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/sgx/main.c
> > b/arch/x86/kernel/cpu/sgx/main.c
> > index 4cdeb915dc86..af68dc1c677b 100644
> > --- a/arch/x86/kernel/cpu/sgx/main.c
> > +++ b/arch/x86/kernel/cpu/sgx/main.c
> > @@ -26,10 +26,9 @@ static DEFINE_XARRAY(sgx_epc_address_space);
> >
> > /*
> > * These variables are part of the state of the reclaimer, and
> > must be accessed
> > - * with sgx_reclaimer_lock acquired.
> > + * with sgx_global_lru.lock acquired.
> > */
> > -static LIST_HEAD(sgx_active_page_list);
> > -static DEFINE_SPINLOCK(sgx_reclaimer_lock);
> > +static struct sgx_epc_lru sgx_global_lru;
> >
> > static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
> >
> > @@ -298,12 +297,12 @@ static void sgx_reclaim_pages(void)
> > int ret;
> > int i;
> >
> > - spin_lock(&sgx_reclaimer_lock);
> > + spin_lock(&sgx_global_lru.lock);
> > for (i = 0; i < SGX_NR_TO_SCAN; i++) {
> > - if (list_empty(&sgx_active_page_list))
> > + if (list_empty(&sgx_global_lru.reclaimable))
> > break;
> >
> > - epc_page = list_first_entry(&sgx_active_page_list,
> > + epc_page =
> > list_first_entry(&sgx_global_lru.reclaimable,
> > struct sgx_epc_page,
> > list);
> > list_del_init(&epc_page->list);
> > encl_page = epc_page->owner;
> > @@ -316,7 +315,7 @@ static void sgx_reclaim_pages(void)
> > */
> > epc_page->flags &=
> > ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> > }
> > - spin_unlock(&sgx_reclaimer_lock);
> > + spin_unlock(&sgx_global_lru.lock);
> >
> > for (i = 0; i < cnt; i++) {
> > epc_page = chunk[i];
> > @@ -339,9 +338,9 @@ static void sgx_reclaim_pages(void)
> > continue;
> >
> > skip:
> > - spin_lock(&sgx_reclaimer_lock);
> > - list_add_tail(&epc_page->list,
> > &sgx_active_page_list);
> > - spin_unlock(&sgx_reclaimer_lock);
> > + spin_lock(&sgx_global_lru.lock);
> > + list_add_tail(&epc_page->list,
> > &sgx_global_lru.reclaimable);
> > + spin_unlock(&sgx_global_lru.lock);
> >
> > kref_put(&encl_page->encl->refcount,
> > sgx_encl_release);
> >
> > @@ -374,7 +373,7 @@ static void sgx_reclaim_pages(void)
> > static bool sgx_should_reclaim(unsigned long watermark)
> > {
> > return atomic_long_read(&sgx_nr_free_pages) < watermark &&
> > - !list_empty(&sgx_active_page_list);
> > + !list_empty(&sgx_global_lru.reclaimable);
> > }
> >
> > /*
> > @@ -427,6 +426,8 @@ static bool __init
> > sgx_page_reclaimer_init(void)
> >
> > ksgxd_tsk = tsk;
> >
> > + sgx_lru_init(&sgx_global_lru);
> > +
> > return true;
> > }
> >
> > @@ -502,10 +503,10 @@ struct sgx_epc_page
> > *__sgx_alloc_epc_page(void)
> > */
> > void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
> > {
> > - spin_lock(&sgx_reclaimer_lock);
> > + spin_lock(&sgx_global_lru.lock);
> > page->flags |= SGX_EPC_PAGE_RECLAIMER_TRACKED;
> > - list_add_tail(&page->list, &sgx_active_page_list);
> > - spin_unlock(&sgx_reclaimer_lock);
> > + list_add_tail(&page->list, &sgx_global_lru.reclaimable);
> > + spin_unlock(&sgx_global_lru.lock);
> > }
> >
> > /**
> > @@ -520,18 +521,18 @@ void sgx_mark_page_reclaimable(struct
> > sgx_epc_page *page)
> > */
> > int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
> > {
> > - spin_lock(&sgx_reclaimer_lock);
> > + spin_lock(&sgx_global_lru.lock);
> > if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
> > /* The page is being reclaimed. */
> > if (list_empty(&page->list)) {
> > - spin_unlock(&sgx_reclaimer_lock);
> > + spin_unlock(&sgx_global_lru.lock);
> > return -EBUSY;
> > }
> >
> > list_del(&page->list);
> > page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
> > }
> > - spin_unlock(&sgx_reclaimer_lock);
> > + spin_unlock(&sgx_global_lru.lock);
> >
> > return 0;
> > }
> > @@ -564,7 +565,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void
> > *owner, bool reclaim)
> > break;
> > }
> >
> > - if (list_empty(&sgx_active_page_list))
> > + if (list_empty(&sgx_global_lru.reclaimable))
> > return ERR_PTR(-ENOMEM);
> >
> > if (!reclaim) {
> > diff --git a/arch/x86/kernel/cpu/sgx/sgx.h
> > b/arch/x86/kernel/cpu/sgx/sgx.h
> > index 5a7e858a8f98..7b208ee8eb45 100644
> > --- a/arch/x86/kernel/cpu/sgx/sgx.h
> > +++ b/arch/x86/kernel/cpu/sgx/sgx.h
> > @@ -83,6 +83,17 @@ static inline void *sgx_get_epc_virt_addr(struct
> > sgx_epc_page *page)
> > return section->virt_addr + index * PAGE_SIZE;
> > }
> >
> > +struct sgx_epc_lru {
> > + spinlock_t lock;
> > + struct list_head reclaimable;
>
> s/reclaimable/list/
It feels to me that once you add the "unreclaimable" struct list_head
field to this struct in the next patch, it would be a bit confusing to
rename this to just "list". What the final struct looks like is
actually not really a nice clean simple queue, but 2 lists - one for
EPC pages which are being tracked by the reclaimer, and one for EPC
pages which are not (such as va pages).
>
> > +};
> > +
> > +static inline void sgx_lru_init(struct sgx_epc_lru *lru)
> > +{
> > + spin_lock_init(&lru->lock);
> > + INIT_LIST_HEAD(&lru->reclaimable);
> > +}
> > +
> > struct sgx_epc_page *__sgx_alloc_epc_page(void);
> > void sgx_free_epc_page(struct sgx_epc_page *page);
> >
> > --
> > 2.37.3
> >
>
> Please also add these:
>
> /*
> * Must be called with queue->lock acquired.
> */
> static inline struct sgx_epc_page *__sgx_epc_queue_push(struct
> sgx_epc_queue *queue,
> struct
> sgx_page *page)
> {
> list_add_tail(&page->list, &queue->list);
> }
>
> /*
> * Must be called with queue->lock acquired.
> */
> static inline struct sgx_epc_page *__sgx_epc_queue_pop(struct
> sgx_epc_queue *queue)
> {
> struct sgx_epc_page *page;
>
> if (list_empty(&queue->list)
> return NULL;
>
> page = list_first_entry(&queue->list, struct sgx_epc_page,
> list);
> list_del_init(&page->list);
>
> return page;
> }
>
> And use them in existing sites. It ensures coherent behavior. You
> should be
> able to replace all uses with either, or combination of them
> (list_move).
>
> BR, Jarkko
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