From: Scott Wood <scottwood@freescale.com> To: Alexander Graf <agraf@suse.de> Cc: <kvm-ppc@vger.kernel.org>, <kvm@vger.kernel.org> Subject: Re: [PATCH 00/33] KVM: PPC: Fix IRQ race in magic page code Date: Tue, 24 Jun 2014 19:21:29 -0500 [thread overview] Message-ID: <1403655689.2435.55.camel@snotra.buserror.net> (raw) In-Reply-To: <53AA0C78.60703@suse.de> On Wed, 2014-06-25 at 01:40 +0200, Alexander Graf wrote: > On 25.06.14 01:15, Scott Wood wrote: > > On Wed, 2014-06-25 at 00:41 +0200, Alexander Graf wrote: > >> On 24.06.14 20:53, Scott Wood wrote: > >>> The timer interrupt works, but I'm not fully convinced that it's a good > >> idea for things like MC events which we also block during critical > >> sections on e500v2. > > Are you concerned about the guest seeing machine checks that are (more) > > asynchronous with the error condition? e500v2 machine checks are always > > asynchronous. From the core manual: > > > > Machine check interrupts are typically caused by a hardware or > > memory subsystem failure or by an attempt to access an invalid > > address. They may be caused indirectly by execution of an > > instruction, but may not be recognized or reported until long > > after the processor has executed past the instruction that > > caused the machine check. As such, machine check interrupts are > > not thought of as synchronous or asynchronous nor as precise or > > imprecise. > > > > I don't think the lag would be a problem, and certainly it's better than > > the current situation. > > So what value would you set the timer to? If the value is too small, we > never finish the critical section. If it's too big, we add lots of jitter. Maybe something like 100us? Single stepping would be better, though. > >> Single stepping is hard enough to get right on interaction between QEMU, > >> KVM and the guest. I didn't really want to make that stuff any more > >> complicated. > > I'm not sure that it would add much complexity. We'd just need to check > > whether any source other than the magic page turned wants DCBR0_IC on, > > to determine whether to exit to userspace or not. > > What if the guest is single stepping itself? How do we determine when to > unset the bit again? When we get out of the critical section? How do we > know what the value was before we set it? Keep track of each requester of single stepping separately, and only ever set the real bit by ORing them. -Scott
WARNING: multiple messages have this Message-ID (diff)
From: Scott Wood <scottwood@freescale.com> To: Alexander Graf <agraf@suse.de> Cc: kvm-ppc@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 00/33] KVM: PPC: Fix IRQ race in magic page code Date: Wed, 25 Jun 2014 00:21:29 +0000 [thread overview] Message-ID: <1403655689.2435.55.camel@snotra.buserror.net> (raw) In-Reply-To: <53AA0C78.60703@suse.de> On Wed, 2014-06-25 at 01:40 +0200, Alexander Graf wrote: > On 25.06.14 01:15, Scott Wood wrote: > > On Wed, 2014-06-25 at 00:41 +0200, Alexander Graf wrote: > >> On 24.06.14 20:53, Scott Wood wrote: > >>> The timer interrupt works, but I'm not fully convinced that it's a good > >> idea for things like MC events which we also block during critical > >> sections on e500v2. > > Are you concerned about the guest seeing machine checks that are (more) > > asynchronous with the error condition? e500v2 machine checks are always > > asynchronous. From the core manual: > > > > Machine check interrupts are typically caused by a hardware or > > memory subsystem failure or by an attempt to access an invalid > > address. They may be caused indirectly by execution of an > > instruction, but may not be recognized or reported until long > > after the processor has executed past the instruction that > > caused the machine check. As such, machine check interrupts are > > not thought of as synchronous or asynchronous nor as precise or > > imprecise. > > > > I don't think the lag would be a problem, and certainly it's better than > > the current situation. > > So what value would you set the timer to? If the value is too small, we > never finish the critical section. If it's too big, we add lots of jitter. Maybe something like 100us? Single stepping would be better, though. > >> Single stepping is hard enough to get right on interaction between QEMU, > >> KVM and the guest. I didn't really want to make that stuff any more > >> complicated. > > I'm not sure that it would add much complexity. We'd just need to check > > whether any source other than the magic page turned wants DCBR0_IC on, > > to determine whether to exit to userspace or not. > > What if the guest is single stepping itself? How do we determine when to > unset the bit again? When we get out of the critical section? How do we > know what the value was before we set it? Keep track of each requester of single stepping separately, and only ever set the real bit by ORing them. -Scott
next prev parent reply other threads:[~2014-06-25 0:21 UTC|newest] Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-06-22 21:23 [PATCH 00/33] KVM: PPC: Fix IRQ race in magic page code Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 01/33] KVM: PPC: Implement kvmppc_xlate for all targets Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 02/33] KVM: PPC: Move kvmppc_ld/st to common code Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 03/33] KVM: PPC: Remove kvmppc_bad_hva() Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 04/33] KVM: PPC: Propagate kvmppc_xlate errors properly Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 05/33] KVM: PPC: Use kvm_read_guest in kvmppc_ld Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 06/33] KVM: PPC: Handle magic page in kvmppc_ld/st Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 07/33] KVM: PPC: Separate loadstore emulation from priv emulation Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 08/33] KVM: PPC: Introduce emulation for unprivileged instructions Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 09/33] KVM: PPC: Move critical section detection to common code Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 10/33] KVM: PPC: Make critical section detection conditional Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 11/33] KVM: PPC: BookE: Use common critical section helper Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 12/33] KVM: PPC: Emulate critical sections when we hit them Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 13/33] KVM: PPC: Expose helper functions for data/inst faults Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 14/33] KVM: PPC: Add std instruction emulation Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 15/33] KVM: PPC: Add stw " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 16/33] KVM: PPC: Add ld " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 17/33] KVM: PPC: Add lwz " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 18/33] KVM: PPC: Add mfcr " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 19/33] KVM: PPC: Add addis " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 20/33] KVM: PPC: Add ori " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 21/33] KVM: PPC: Add and " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 22/33] KVM: PPC: Add andi. " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 23/33] KVM: PPC: Add or " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 24/33] KVM: PPC: Add cmpwi/cmpdi " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 25/33] KVM: PPC: Add bc " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 26/33] KVM: PPC: Add mtcrf " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 27/33] KVM: PPC: Add xor " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 28/33] KVM: PPC: Add oris " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 29/33] KVM: PPC: Add rldicr/rldicl/rldic " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 30/33] KVM: PPC: Add rlwimi " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 31/33] KVM: PPC: Add rlwinm " Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 32/33] KVM: PPC: Handle NV registers in emulated critical sections Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-22 21:23 ` [PATCH 33/33] KVM: PPC: Enable critical section emulation Alexander Graf 2014-06-22 21:23 ` Alexander Graf 2014-06-24 18:53 ` [PATCH 00/33] KVM: PPC: Fix IRQ race in magic page code Scott Wood 2014-06-24 18:53 ` Scott Wood 2014-06-24 22:41 ` Alexander Graf 2014-06-24 22:41 ` Alexander Graf 2014-06-24 23:15 ` Scott Wood 2014-06-24 23:15 ` Scott Wood 2014-06-24 23:40 ` Alexander Graf 2014-06-24 23:40 ` Alexander Graf 2014-06-25 0:21 ` Scott Wood [this message] 2014-06-25 0:21 ` Scott Wood 2014-07-28 14:10 ` Alexander Graf 2014-07-28 14:10 ` Alexander Graf
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