Date: Wed, 1 Feb 2023 12:27:22 GMT From: =?utf-8?Q?Corvin=20K=C3=B6hne?= <corvink@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 892feec2211d - main - vmm: avoid spurious rendezvous Message-ID: <202302011227.311CRMjk017681@gitrepo.freebsd.org>
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The branch main has been updated by corvink: URL: https://cgit.FreeBSD.org/src/commit/?id=892feec2211d0dbd58252a34d78dbcb2d5dd7593 commit 892feec2211d0dbd58252a34d78dbcb2d5dd7593 Author: Corvin Köhne <corvink@FreeBSD.org> AuthorDate: 2022-11-15 10:53:49 +0000 Commit: Corvin Köhne <corvink@FreeBSD.org> CommitDate: 2023-02-01 11:36:36 +0000 vmm: avoid spurious rendezvous A vcpu only checks if a rendezvous is in progress or not to decide if it should handle a rendezvous. This could lead to spurios rendezvous where a vcpu tries a handle a rendezvous it isn't part of. This situation is properly handled by vm_handle_rendezvous but it could potentially degrade the performance. Avoid that by an early check if the vcpu is part of the rendezvous or not. At the moment, rendezvous are only used to spin up application processors and to send ioapic interrupts. Spinning up application processors is done in the guest boot phase by sending INIT SIPI sequences to single vcpus. This is known to cause spurious rendezvous and only occurs in the boot phase. Sending ioapic interrupts is rare because modern guest will use msi and the rendezvous is always send to all vcpus. Reviewed by: jhb MFC after: 1 week Sponsored by: Beckhoff Automation GmbH & Co. KG Differential Revision: https://reviews.freebsd.org/D37390 --- sys/amd64/include/vmm.h | 14 ++++++++++---- sys/amd64/vmm/amd/svm.c | 2 +- sys/amd64/vmm/intel/vmx.c | 2 +- sys/amd64/vmm/vmm.c | 3 ++- 4 files changed, 14 insertions(+), 7 deletions(-) diff --git a/sys/amd64/include/vmm.h b/sys/amd64/include/vmm.h index 67730cc22980..bd6510b92527 100644 --- a/sys/amd64/include/vmm.h +++ b/sys/amd64/include/vmm.h @@ -159,7 +159,7 @@ struct pmap; enum snapshot_req; struct vm_eventinfo { - void *rptr; /* rendezvous cookie */ + cpuset_t *rptr; /* rendezvous cookie */ int *sptr; /* suspend cookie */ int *iptr; /* reqidle cookie */ }; @@ -331,10 +331,16 @@ void vm_await_start(struct vm *vm, const cpuset_t *waiting); #endif /* _SYS__CPUSET_H_ */ static __inline int -vcpu_rendezvous_pending(struct vm_eventinfo *info) +vcpu_rendezvous_pending(struct vcpu *vcpu, struct vm_eventinfo *info) { - - return (*((uintptr_t *)(info->rptr)) != 0); + /* + * This check isn't done with atomic operations or under a lock because + * there's no need to. If the vcpuid bit is set, the vcpu is part of a + * rendezvous and the bit won't be cleared until the vcpu enters the + * rendezvous. On rendezvous exit, the cpuset is cleared and the vcpu + * will see an empty cpuset. So, the races are harmless. + */ + return (CPU_ISSET(vcpu_vcpuid(vcpu), info->rptr)); } static __inline int diff --git a/sys/amd64/vmm/amd/svm.c b/sys/amd64/vmm/amd/svm.c index 2448501401e3..ee1154ef85b6 100644 --- a/sys/amd64/vmm/amd/svm.c +++ b/sys/amd64/vmm/amd/svm.c @@ -2053,7 +2053,7 @@ svm_run(void *vcpui, register_t rip, pmap_t pmap, struct vm_eventinfo *evinfo) break; } - if (vcpu_rendezvous_pending(evinfo)) { + if (vcpu_rendezvous_pending(vcpu->vcpu, evinfo)) { enable_gintr(); vm_exit_rendezvous(vcpu->vcpu, state->rip); break; diff --git a/sys/amd64/vmm/intel/vmx.c b/sys/amd64/vmm/intel/vmx.c index 4b65e254cc91..fa94c707001c 100644 --- a/sys/amd64/vmm/intel/vmx.c +++ b/sys/amd64/vmm/intel/vmx.c @@ -3071,7 +3071,7 @@ vmx_run(void *vcpui, register_t rip, pmap_t pmap, struct vm_eventinfo *evinfo) break; } - if (vcpu_rendezvous_pending(evinfo)) { + if (vcpu_rendezvous_pending(vcpu->vcpu, evinfo)) { enable_intr(); vm_exit_rendezvous(vcpu->vcpu, rip); break; diff --git a/sys/amd64/vmm/vmm.c b/sys/amd64/vmm/vmm.c index 24f97a9244f0..7327bf6f40be 100644 --- a/sys/amd64/vmm/vmm.c +++ b/sys/amd64/vmm/vmm.c @@ -1438,6 +1438,7 @@ vm_handle_rendezvous(struct vcpu *vcpu) if (CPU_CMP(&vm->rendezvous_req_cpus, &vm->rendezvous_done_cpus) == 0) { VMM_CTR0(vcpu, "Rendezvous completed"); + CPU_ZERO(&vm->rendezvous_req_cpus); vm->rendezvous_func = NULL; wakeup(&vm->rendezvous_func); break; @@ -1858,7 +1859,7 @@ vm_run(struct vcpu *vcpu, struct vm_exit *vme_user) pmap = vmspace_pmap(vm->vmspace); vme = &vcpu->exitinfo; - evinfo.rptr = &vm->rendezvous_func; + evinfo.rptr = &vm->rendezvous_req_cpus; evinfo.sptr = &vm->suspend; evinfo.iptr = &vcpu->reqidle; restart:
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