From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jes Sorensen Date: Thu, 16 Apr 2009 08:43:48 +0000 Subject: Re: switching from KVM guest to the host .... TLBs not present? Message-Id: <49E6EFC4.7040205@sgi.com> MIME-Version: 1 Content-Type: multipart/mixed; boundary="------------050109030004000805070503" List-Id: References: <49DE0856.8010700@sgi.com> In-Reply-To: <49DE0856.8010700@sgi.com> To: kvm-ia64@vger.kernel.org This is a multi-part message in MIME format. --------------050109030004000805070503 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Avi Kivity wrote: > Applied, but I note that entering the guest with any lock held is > problematic, as the guest may spend an arbitrary amount of time in guest > mode. Really, entering the guest is almost exactly like exiting to > userspace. Hi Avi, I had a look at this and reworked the locking some, so we don't hold the slots_lock when entering the guest. How does this look? Xiantao any thoughts of whether it's unsafe to call kvm_vcpu_post_transition without holding that semaphore? I believe it should be fine. I am still seeing issues where the host can get a lock timeout when running large guests, but the situation seems to be better with this patch applied. Cheers, Jes --------------050109030004000805070503 Content-Type: text/x-patch; name="0002-kvm-ia64-reorder-run-locking.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="0002-kvm-ia64-reorder-run-locking.patch" Reorder locking to avoid holding the slots_lock when entering the guest. Signed-off-by: Jes Sorensen --- arch/ia64/kvm/kvm-ia64.c | 64 ++++++++++++++++++++++++----------------------- 1 file changed, 33 insertions(+), 31 deletions(-) Index: linux-2.6.git/arch/ia64/kvm/kvm-ia64.c =================================================================== --- linux-2.6.git.orig/arch/ia64/kvm/kvm-ia64.c +++ linux-2.6.git/arch/ia64/kvm/kvm-ia64.c @@ -580,34 +580,22 @@ vti_set_rr6(vcpu->arch.vmm_rr); return kvm_insert_vmm_mapping(vcpu); } + static void kvm_vcpu_post_transition(struct kvm_vcpu *vcpu) { kvm_purge_vmm_mapping(vcpu); vti_set_rr6(vcpu->arch.host_rr6); } -static int vti_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) +static int __vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) { union context *host_ctx, *guest_ctx; int r; - /*Get host and guest context with guest address space.*/ - host_ctx = kvm_get_host_context(vcpu); - guest_ctx = kvm_get_guest_context(vcpu); - - r = kvm_vcpu_pre_transition(vcpu); - if (r < 0) - goto out; - kvm_vmm_info->tramp_entry(host_ctx, guest_ctx); - kvm_vcpu_post_transition(vcpu); - r = 0; -out: - return r; -} - -static int __vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) -{ - int r; + /* + * down_read() may sleep and return with interrupts enabled + */ + down_read(&vcpu->kvm->slots_lock); again: if (signal_pending(current)) { @@ -616,23 +604,28 @@ goto out; } - /* - * down_read() may sleep and return with interrupts enabled - */ - down_read(&vcpu->kvm->slots_lock); - preempt_disable(); local_irq_disable(); + /*Get host and guest context with guest address space.*/ + host_ctx = kvm_get_host_context(vcpu); + guest_ctx = kvm_get_guest_context(vcpu); + vcpu->guest_mode = 1; + + r = kvm_vcpu_pre_transition(vcpu); + if (r < 0) + goto vcpu_run_fail; + + up_read(&vcpu->kvm->slots_lock); kvm_guest_enter(); - r = vti_vcpu_run(vcpu, kvm_run); - if (r < 0) { - local_irq_enable(); - preempt_enable(); - kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY; - goto out; - } + + /* + * Transition to the guest + */ + kvm_vmm_info->tramp_entry(host_ctx, guest_ctx); + + kvm_vcpu_post_transition(vcpu); vcpu->arch.launched = 1; vcpu->guest_mode = 0; @@ -646,9 +639,10 @@ */ barrier(); kvm_guest_exit(); - up_read(&vcpu->kvm->slots_lock); preempt_enable(); + down_read(&vcpu->kvm->slots_lock); + r = kvm_handle_exit(kvm_run, vcpu); if (r > 0) { @@ -657,12 +651,20 @@ } out: + up_read(&vcpu->kvm->slots_lock); if (r > 0) { kvm_resched(vcpu); + down_read(&vcpu->kvm->slots_lock); goto again; } return r; + +vcpu_run_fail: + local_irq_enable(); + preempt_enable(); + kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY; + goto out; } static void kvm_set_mmio_data(struct kvm_vcpu *vcpu) --------------050109030004000805070503--