[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] RFC: mem_event: use wait queue when ring is full
Olaf, two questions here - do you have any insight for events caused by foreign mappings? Those will be lost with a full ring, with or without wait queues - we have posted a patch (twice) previously, with changes to ring management, most importantly sending guest vcpus to sleep when space in the ring is < d->max_vcpus. I see these two patches as complementary. What is your take? Thanks, Andres > Date: Tue, 22 Nov 2011 22:13:24 +0100 > From: Olaf Hering <olaf@xxxxxxxxx> > To: xen-devel@xxxxxxxxxxxxxxxxxxx > Subject: [Xen-devel] [PATCH 2 of 3] RFC: mem_event: use wait queue > when ring is full > Message-ID: <de6860cb9205b68d1287.1321996404@xxxxxxxxxxxx> > Content-Type: text/plain; charset="us-ascii" > > # HG changeset patch > # User Olaf Hering <olaf@xxxxxxxxx> > # Date 1321996145 -3600 > # Node ID de6860cb9205b68d1287482288d1b7b9d0255609 > # Parent d347a8a36d2e7951f98a3d22866dce004484d95f > RFC: mem_event: use wait queue when ring is full > > CAUTION: while the patch by itself is supposed to be complete, > the added usage of waitqueues will lead to sudden host reboots! > > > This change is based on an idea/patch from Adin Scannell. > > If the ring is full, put the current vcpu to sleep if it belongs to the > target domain. The wakeup happens in the p2m_*_resume functions. > A request from another domain will use the existing ->req_producers > functionality because sleeping is not possible if the vcpu does not > belong to the target domain. > > This change fixes also a bug in p2m_mem_paging_drop_page(). Up to now a > full ring will lead to harmless inconsistency in the pager, > > v2: > - p2m_mem_paging_populate: move vcpu_pause after put_request, otherwise > the > vcpu will not wake_up after a wait_event because the pause_count was > increased twice. Fixes guest hangs. > - update free space check in _mem_event_put_request() > - simplify mem_event_put_request() > > Signed-off-by: Olaf Hering <olaf@xxxxxxxxx> > > diff -r d347a8a36d2e -r de6860cb9205 xen/arch/x86/hvm/hvm.c > --- a/xen/arch/x86/hvm/hvm.c > +++ b/xen/arch/x86/hvm/hvm.c > @@ -4099,7 +4099,7 @@ static int hvm_memory_event_traps(long p > return 1; > > rc = mem_event_check_ring(d, &d->mem_event->mem_access); > - if ( rc ) > + if ( rc < 0 ) > return rc; > > memset(&req, 0, sizeof(req)); > diff -r d347a8a36d2e -r de6860cb9205 xen/arch/x86/mm/mem_event.c > --- a/xen/arch/x86/mm/mem_event.c > +++ b/xen/arch/x86/mm/mem_event.c > @@ -23,6 +23,7 @@ > > #include <asm/domain.h> > #include <xen/event.h> > +#include <xen/wait.h> > #include <asm/p2m.h> > #include <asm/mem_event.h> > #include <asm/mem_paging.h> > @@ -39,6 +40,7 @@ > > static int mem_event_enable(struct domain *d, > xen_domctl_mem_event_op_t *mec, > + int mem_event_bit, > struct mem_event_domain *med) > { > int rc; > @@ -107,8 +109,12 @@ static int mem_event_enable(struct domai > > mem_event_ring_lock_init(med); > > + med->mem_event_bit = mem_event_bit; > + > + init_waitqueue_head(&med->wq); > + > /* Wake any VCPUs paused for memory events */ > - mem_event_unpause_vcpus(d); > + mem_event_unpause_vcpus(d, med); > > return 0; > > @@ -124,6 +130,9 @@ static int mem_event_enable(struct domai > > static int mem_event_disable(struct mem_event_domain *med) > { > + if (!list_empty(&med->wq.list)) > + return -EBUSY; > + > unmap_domain_page(med->ring_page); > med->ring_page = NULL; > > @@ -133,13 +142,21 @@ static int mem_event_disable(struct mem_ > return 0; > } > > -void mem_event_put_request(struct domain *d, struct mem_event_domain > *med, mem_event_request_t *req) > +static int _mem_event_put_request(struct domain *d, struct > mem_event_domain *med, mem_event_request_t *req) > { > mem_event_front_ring_t *front_ring; > + int free_requests; > RING_IDX req_prod; > > mem_event_ring_lock(med); > > + free_requests = RING_FREE_REQUESTS(&med->front_ring); > + /* A request was eventually claimed in mem_event_check_ring() */ > + if ((current->domain == d && free_requests <= med->req_producers) || > !free_requests) { > + mem_event_ring_unlock(med); > + return 0; > + } > + > front_ring = &med->front_ring; > req_prod = front_ring->req_prod_pvt; > > @@ -155,6 +172,20 @@ void mem_event_put_request(struct domain > mem_event_ring_unlock(med); > > notify_via_xen_event_channel(d, med->xen_port); > + > + return 1; > +} > + > +void mem_event_put_request(struct domain *d, struct mem_event_domain > *med, mem_event_request_t *req) > +{ > + /* Go to sleep if request came from guest */ > + if (current->domain == d) { > + wait_event(med->wq, _mem_event_put_request(d, med, req)); > + return; > + } > + /* Ring was full anyway, unable to sleep in non-guest context */ > + if (!_mem_event_put_request(d, med, req)) > + printk("Failed to put memreq: d %u t %x f %x gfn %lx\n", > d->domain_id, req->type, req->flags, (unsigned long)req->gfn); > } > > void mem_event_get_response(struct mem_event_domain *med, > mem_event_response_t *rsp) > @@ -178,21 +209,27 @@ void mem_event_get_response(struct mem_e > mem_event_ring_unlock(med); > } > > -void mem_event_unpause_vcpus(struct domain *d) > +void mem_event_unpause_vcpus(struct domain *d, struct mem_event_domain > *med) > { > struct vcpu *v; > > for_each_vcpu ( d, v ) > - if ( test_and_clear_bit(_VPF_mem_event, &v->pause_flags) ) > + if ( test_and_clear_bit(med->mem_event_bit, &v->pause_flags) ) > vcpu_wake(v); > } > > -void mem_event_mark_and_pause(struct vcpu *v) > +void mem_event_mark_and_pause(struct vcpu *v, struct mem_event_domain > *med) > { > - set_bit(_VPF_mem_event, &v->pause_flags); > + set_bit(med->mem_event_bit, &v->pause_flags); > vcpu_sleep_nosync(v); > } > > +/** > + * mem_event_put_req_producers - Release a claimed slot > + * @med: mem_event ring > + * > + * mem_event_put_req_producers() releases a claimed slot in the mem_event > ring. > + */ > void mem_event_put_req_producers(struct mem_event_domain *med) > { > mem_event_ring_lock(med); > @@ -200,9 +237,26 @@ void mem_event_put_req_producers(struct > mem_event_ring_unlock(med); > } > > +/** > + * mem_event_check_ring - Check state of a mem_event ring > + * @d: guest domain > + * @med: mem_event ring > + * > + * Return codes: < 0: the ring is not yet configured > + * 0: the ring has some room > + * > 0: the ring is full > + * > + * mem_event_check_ring() checks the state of the given mem_event ring. > + * If the current vcpu belongs to the guest domain, the function assumes > that > + * mem_event_put_request() will sleep until the ring has room again. > + * > + * If the current vcpu does not belong to the target domain the caller > must try > + * again until there is room. A slot is claimed and the caller can place > a > + * request. If the caller does not need to send a request, the claimed > slot has > + * to be released with mem_event_put_req_producers(). > + */ > int mem_event_check_ring(struct domain *d, struct mem_event_domain *med) > { > - struct vcpu *curr = current; > int free_requests; > int ring_full = 1; > > @@ -218,8 +272,8 @@ int mem_event_check_ring(struct domain * > ring_full = 0; > } > > - if ( ring_full && (curr->domain == d) ) > - mem_event_mark_and_pause(curr); > + if ( current->domain == d ) > + ring_full = 0; > > mem_event_ring_unlock(med); > > @@ -287,7 +341,7 @@ int mem_event_domctl(struct domain *d, x > if ( p2m->pod.entry_count ) > break; > > - rc = mem_event_enable(d, mec, med); > + rc = mem_event_enable(d, mec, _VPF_me_mem_paging, med); > } > break; > > @@ -326,7 +380,7 @@ int mem_event_domctl(struct domain *d, x > if ( boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ) > break; > > - rc = mem_event_enable(d, mec, med); > + rc = mem_event_enable(d, mec, _VPF_me_mem_access, med); > } > break; > > diff -r d347a8a36d2e -r de6860cb9205 xen/arch/x86/mm/mem_sharing.c > --- a/xen/arch/x86/mm/mem_sharing.c > +++ b/xen/arch/x86/mm/mem_sharing.c > @@ -253,19 +253,11 @@ static void mem_sharing_audit(void) > #endif > > > -static struct page_info* mem_sharing_alloc_page(struct domain *d, > - unsigned long gfn) > +static void mem_sharing_notify_helper(struct domain *d, unsigned long > gfn) > { > - struct page_info* page; > struct vcpu *v = current; > mem_event_request_t req; > > - page = alloc_domheap_page(d, 0); > - if(page != NULL) return page; > - > - memset(&req, 0, sizeof(req)); > - req.type = MEM_EVENT_TYPE_SHARED; > - > if ( v->domain != d ) > { > /* XXX This path needs some attention. For now, just fail > foreign > @@ -275,20 +267,20 @@ static struct page_info* mem_sharing_all > gdprintk(XENLOG_ERR, > "Failed alloc on unshare path for foreign (%d) > lookup\n", > d->domain_id); > - return page; > + return; > } > > - vcpu_pause_nosync(v); > - req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED; > + if (mem_event_check_ring(d, &d->mem_event->mem_share) < 0) > + return; > > - if(mem_event_check_ring(d, &d->mem_event->mem_share)) return page; > - > + memset(&req, 0, sizeof(req)); > + req.type = MEM_EVENT_TYPE_SHARED; > + req.flags = MEM_EVENT_FLAG_VCPU_PAUSED; > req.gfn = gfn; > req.p2mt = p2m_ram_shared; > req.vcpu_id = v->vcpu_id; > mem_event_put_request(d, &d->mem_event->mem_share, &req); > - > - return page; > + vcpu_pause_nosync(v); > } > > unsigned int mem_sharing_get_nr_saved_mfns(void) > @@ -653,7 +645,7 @@ gfn_found: > if(ret == 0) goto private_page_found; > > old_page = page; > - page = mem_sharing_alloc_page(d, gfn); > + page = alloc_domheap_page(d, 0); > if(!page) > { > /* We've failed to obtain memory for private page. Need to re-add > the > @@ -661,6 +653,7 @@ gfn_found: > list_add(&gfn_info->list, &hash_entry->gfns); > put_gfn(d, gfn); > shr_unlock(); > + mem_sharing_notify_helper(d, gfn); > return -ENOMEM; > } > > diff -r d347a8a36d2e -r de6860cb9205 xen/arch/x86/mm/p2m.c > --- a/xen/arch/x86/mm/p2m.c > +++ b/xen/arch/x86/mm/p2m.c > @@ -884,17 +884,13 @@ void p2m_mem_paging_drop_page(struct dom > struct vcpu *v = current; > mem_event_request_t req; > > - /* Check that there's space on the ring for this request */ > - if ( mem_event_check_ring(d, &d->mem_event->mem_paging) == 0) > - { > - /* Send release notification to pager */ > - memset(&req, 0, sizeof(req)); > - req.flags |= MEM_EVENT_FLAG_DROP_PAGE; > - req.gfn = gfn; > - req.vcpu_id = v->vcpu_id; > + /* Send release notification to pager */ > + memset(&req, 0, sizeof(req)); > + req.flags = MEM_EVENT_FLAG_DROP_PAGE; > + req.gfn = gfn; > + req.vcpu_id = v->vcpu_id; > > - mem_event_put_request(d, &d->mem_event->mem_paging, &req); > - } > + mem_event_put_request(d, &d->mem_event->mem_paging, &req); > } > > /** > @@ -952,7 +948,6 @@ void p2m_mem_paging_populate(struct doma > /* Pause domain if request came from guest and gfn has paging type */ > if ( p2m_is_paging(p2mt) && v->domain == d ) > { > - vcpu_pause_nosync(v); > req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED; > } > /* No need to inform pager if the gfn is not in the page-out path */ > @@ -969,6 +964,10 @@ void p2m_mem_paging_populate(struct doma > req.vcpu_id = v->vcpu_id; > > mem_event_put_request(d, &d->mem_event->mem_paging, &req); > + > + /* Pause guest after put_request to allow wake_up after wait_event */ > + if ( req.flags & MEM_EVENT_FLAG_VCPU_PAUSED ) > + vcpu_pause_nosync(v); > } > > /** > @@ -1071,8 +1070,8 @@ void p2m_mem_paging_resume(struct domain > if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED ) > vcpu_unpause(d->vcpu[rsp.vcpu_id]); > > - /* Unpause any domains that were paused because the ring was full */ > - mem_event_unpause_vcpus(d); > + /* Unpause all vcpus that were paused because the ring was full */ > + wake_up(&d->mem_event->mem_paging.wq); > } > > void p2m_mem_access_check(unsigned long gpa, bool_t gla_valid, unsigned > long gla, > @@ -1111,7 +1110,7 @@ void p2m_mem_access_check(unsigned long > "Memory access permissions failure, no mem_event > listener: pausing VCPU %d, dom %d\n", > v->vcpu_id, d->domain_id); > > - mem_event_mark_and_pause(v); > + mem_event_mark_and_pause(v, &d->mem_event->mem_access); > } > else > { > @@ -1131,8 +1130,7 @@ void p2m_mem_access_check(unsigned long > req.reason = MEM_EVENT_REASON_VIOLATION; > > /* Pause the current VCPU unconditionally */ > - vcpu_pause_nosync(v); > - req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED; > + req.flags = MEM_EVENT_FLAG_VCPU_PAUSED; > > /* Send request to mem event */ > req.gfn = gfn; > @@ -1148,6 +1146,7 @@ void p2m_mem_access_check(unsigned long > mem_event_put_request(d, &d->mem_event->mem_access, &req); > > /* VCPU paused, mem event request sent */ > + vcpu_pause_nosync(v); > } > > void p2m_mem_access_resume(struct p2m_domain *p2m) > @@ -1161,9 +1160,11 @@ void p2m_mem_access_resume(struct p2m_do > if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED ) > vcpu_unpause(d->vcpu[rsp.vcpu_id]); > > - /* Unpause any domains that were paused because the ring was full or > no listener > - * was available */ > - mem_event_unpause_vcpus(d); > + /* Wakeup all vcpus waiting because the ring was full */ > + wake_up(&d->mem_event->mem_access.wq); > + > + /* Unpause all vcpus that were paused because no listener was > available */ > + mem_event_unpause_vcpus(d, &d->mem_event->mem_access); > } > > > diff -r d347a8a36d2e -r de6860cb9205 xen/include/asm-x86/mem_event.h > --- a/xen/include/asm-x86/mem_event.h > +++ b/xen/include/asm-x86/mem_event.h > @@ -25,12 +25,12 @@ > #define __MEM_EVENT_H__ > > /* Pauses VCPU while marking pause flag for mem event */ > -void mem_event_mark_and_pause(struct vcpu *v); > +void mem_event_mark_and_pause(struct vcpu *v, struct mem_event_domain > *med); > int mem_event_check_ring(struct domain *d, struct mem_event_domain *med); > void mem_event_put_req_producers(struct mem_event_domain *med); > void mem_event_put_request(struct domain *d, struct mem_event_domain > *med, mem_event_request_t *req); > void mem_event_get_response(struct mem_event_domain *med, > mem_event_response_t *rsp); > -void mem_event_unpause_vcpus(struct domain *d); > +void mem_event_unpause_vcpus(struct domain *d, struct mem_event_domain > *med); > > int mem_event_domctl(struct domain *d, xen_domctl_mem_event_op_t *mec, > XEN_GUEST_HANDLE(void) u_domctl); > diff -r d347a8a36d2e -r de6860cb9205 xen/include/xen/sched.h > --- a/xen/include/xen/sched.h > +++ b/xen/include/xen/sched.h > @@ -14,6 +14,7 @@ > #include <xen/nodemask.h> > #include <xen/radix-tree.h> > #include <xen/multicall.h> > +#include <xen/wait.h> > #include <public/xen.h> > #include <public/domctl.h> > #include <public/sysctl.h> > @@ -192,6 +193,10 @@ struct mem_event_domain > mem_event_front_ring_t front_ring; > /* event channel port (vcpu0 only) */ > int xen_port; > + /* mem_event bit for vcpu->pause_flags */ > + int mem_event_bit; > + /* list of vcpus waiting for room in the ring */ > + struct waitqueue_head wq; > }; > > struct mem_event_per_domain > @@ -615,9 +620,12 @@ static inline struct domain *next_domain > /* VCPU affinity has changed: migrating to a new CPU. */ > #define _VPF_migrating 3 > #define VPF_migrating (1UL<<_VPF_migrating) > - /* VCPU is blocked on memory-event ring. */ > -#define _VPF_mem_event 4 > -#define VPF_mem_event (1UL<<_VPF_mem_event) > + /* VCPU is blocked on mem_paging ring. */ > +#define _VPF_me_mem_paging 4 > +#define VPF_me_mem_paging (1UL<<_VPF_me_mem_paging) > + /* VCPU is blocked on mem_access ring. */ > +#define _VPF_me_mem_access 5 > +#define VPF_me_mem_access (1UL<<_VPF_me_mem_access) > > static inline int vcpu_runnable(struct vcpu *v) > { > > > > ------------------------------ > > Message: 3 > Date: Tue, 22 Nov 2011 22:15:19 +0100 > From: Olaf Hering <olaf@xxxxxxxxx> > To: Keir Fraser <keir.xen@xxxxxxxxx> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [Xen-devel] Need help with fixing the Xen waitqueue > feature > Message-ID: <20111122211519.GA1039@xxxxxxxxx> > Content-Type: text/plain; charset=utf-8 > > On Tue, Nov 22, Olaf Hering wrote: > >> On Tue, Nov 22, Keir Fraser wrote: >> >> > Could it have ended up on the waitqueue? >> >> Unlikely, but I will add checks for that as well. > > I posted three changes which make use of the wait queues. > For some reason the code at the very end of p2m_mem_paging_populate() > triggers when d is dom0, so its vcpu is put to sleep. > > > Olaf > > > > ------------------------------ > > Message: 4 > Date: Tue, 22 Nov 2011 21:53:35 +0000 > From: Keir Fraser <keir.xen@xxxxxxxxx> > To: Olaf Hering <olaf@xxxxxxxxx> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx > Subject: Re: [Xen-devel] Need help with fixing the Xen waitqueue > feature > Message-ID: <CAF1CA5F.2560C%keir.xen@xxxxxxxxx> > Content-Type: text/plain; charset="US-ASCII" > > On 22/11/2011 21:15, "Olaf Hering" <olaf@xxxxxxxxx> wrote: > >> On Tue, Nov 22, Olaf Hering wrote: >> >>> On Tue, Nov 22, Keir Fraser wrote: >>> >>>> Could it have ended up on the waitqueue? >>> >>> Unlikely, but I will add checks for that as well. >> >> I posted three changes which make use of the wait queues. >> For some reason the code at the very end of p2m_mem_paging_populate() >> triggers when d is dom0, so its vcpu is put to sleep. > > We obviously can't have dom0 going to sleep on paging work. This, at > least, > isn't a wait-queue bug. > >> Olaf > > > > > > ------------------------------ > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel > > > End of Xen-devel Digest, Vol 81, Issue 296 > ****************************************** > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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