From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] x86: handle double and triple faults for every exception Date: Wed, 30 Apr 2008 12:42:15 +0200 Message-ID: <48184D07.2090409@siemens.com> References: <1209481325-14892-1-git-send-email-joerg.roedel@amd.com> <48183198.1050508@siemens.com> <48184108.7050000@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel@lists.sourceforge.net To: Avi Kivity Return-path: In-Reply-To: <48184108.7050000@qumranet.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces@lists.sourceforge.net Errors-To: kvm-devel-bounces@lists.sourceforge.net List-Id: kvm.vger.kernel.org Avi Kivity wrote: > Jan Kiszka wrote: >> Joerg Roedel wrote: >> >>> The current KVM x86 exception code handles double and triple faults >>> only for >>> page fault exceptions. This patch extends this detection for every >>> exception >>> that gets queued for the guest. >>> >>> Signed-off-by: Joerg Roedel >>> Cc: Jan Kiszka >>> --- >>> arch/x86/kvm/x86.c | 31 +++++++++++++++++-------------- >>> 1 files changed, 17 insertions(+), 14 deletions(-) >>> >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>> index 578a0c1..c05aa32 100644 >>> --- a/arch/x86/kvm/x86.c >>> +++ b/arch/x86/kvm/x86.c >>> @@ -144,9 +144,21 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, >>> u64 data) >>> } >>> EXPORT_SYMBOL_GPL(kvm_set_apic_base); >>> >>> +static void handle_multiple_faults(struct kvm_vcpu *vcpu) >>> +{ >>> + if (vcpu->arch.exception.nr != DF_VECTOR) { >>> + vcpu->arch.exception.nr = DF_VECTOR; >>> + vcpu->arch.exception.error_code = 0; >>> + } else >>> + set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests); >>> +} >>> + >>> void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr) >>> { >>> - WARN_ON(vcpu->arch.exception.pending); >>> + if (vcpu->arch.exception.pending) { >>> + handle_multiple_faults(vcpu); >>> + return; >>> + } >>> vcpu->arch.exception.pending = true; >>> vcpu->arch.exception.has_error_code = false; >>> vcpu->arch.exception.nr = nr; >>> @@ -157,25 +169,16 @@ void kvm_inject_page_fault(struct kvm_vcpu >>> *vcpu, unsigned long addr, >>> u32 error_code) >>> { >>> ++vcpu->stat.pf_guest; >>> - if (vcpu->arch.exception.pending) { >>> - if (vcpu->arch.exception.nr == PF_VECTOR) { >>> - printk(KERN_DEBUG "kvm: inject_page_fault:" >>> - " double fault 0x%lx\n", addr); >>> - vcpu->arch.exception.nr = DF_VECTOR; >>> - vcpu->arch.exception.error_code = 0; >>> - } else if (vcpu->arch.exception.nr == DF_VECTOR) { >>> - /* triple fault -> shutdown */ >>> - set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests); >>> - } >>> - return; >>> - } >>> vcpu->arch.cr2 = addr; >>> kvm_queue_exception_e(vcpu, PF_VECTOR, error_code); >>> } >>> >>> void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 >>> error_code) >>> { >>> - WARN_ON(vcpu->arch.exception.pending); >>> + if (vcpu->arch.exception.pending) { >>> + handle_multiple_faults(vcpu); >>> + return; >>> + } >>> vcpu->arch.exception.pending = true; >>> vcpu->arch.exception.has_error_code = true; >>> vcpu->arch.exception.nr = nr; >>> >> >> And here is an add-on patch to fix reset-on-triple-fault: >> >> >> Clear the pending original exception when raising a triple fault. This >> allows to re-use the vcpu instance, e.g. after a reset which is >> typically issued as reaction on the triple fault. >> >> Signed-off-by: Jan Kiszka >> >> --- >> arch/x86/kvm/x86.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> Index: b/arch/x86/kvm/x86.c >> =================================================================== >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -149,8 +149,10 @@ static void handle_multiple_faults(struc >> if (vcpu->arch.exception.nr != DF_VECTOR) { >> vcpu->arch.exception.nr = DF_VECTOR; >> vcpu->arch.exception.error_code = 0; >> - } else >> + } else { >> set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests); >> + vcpu->arch.exception.pending = false; >> + } >> } >> >> void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr) >> >> > > There's a bigger problem here. The exception queue is hidden state that > qemu and load and save. Could you elaborate a bit on what the problematic scenario precisely is (that pending triple faults would not be saved/restored while pending exceptions are?), and if I/we can do anything to resolve it? Jan -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone