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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Oliver Upton <oupton@google.com>, Peter Shier <pshier@google.com>
Subject: Re: [PATCH 09/13] KVM: nVMX: Prioritize SMI over nested IRQ/NMI
Date: Wed, 29 Apr 2020 13:06:29 -0700	[thread overview]
Message-ID: <20200429200629.GH15992@linux.intel.com> (raw)
In-Reply-To: <20200429145040.GA15992@linux.intel.com>

On Wed, Apr 29, 2020 at 07:50:40AM -0700, Sean Christopherson wrote:
> On Tue, Apr 28, 2020 at 04:16:16PM -0700, Jim Mattson wrote:
> > On Tue, Apr 28, 2020 at 3:59 PM Sean Christopherson
> > <sean.j.christopherson@intel.com> wrote:
> > >
> > > On Tue, Apr 28, 2020 at 03:04:02PM -0700, Jim Mattson wrote:
> > > > From the SDM, volume 3:
> > > >
> > > > • System-management interrupts (SMIs), INIT signals, and higher
> > > > priority events take priority over MTF VM exits.
> > > >
> > > > I think this block needs to be moved up.
> > >
> > > Hrm.  It definitely needs to be moved above the preemption timer, though I
> > > can't find any public documentation about the preemption timer's priority.
> > > Preemption timer is lower priority than MTF, ergo it's not in the same
> > > class as SMI.
> > >
> > > Regarding SMI vs. MTF and #DB trap, to actually prioritize SMIs above MTF
> > > and #DBs, we'd need to save/restore MTF and pending #DBs via SMRAM.  I
> > > think it makes sense to take the easy road and keep SMI after the traps,
> > > with a comment to say it's technically wrong but not worth fixing.
> > 
> > Pending debug exceptions should just go in the pending debug
> > exceptions field. End of story and end of complications. I don't
> > understand why kvm is so averse to using this field the way it was
> > intended.
> 
> Ah, it took my brain a bit to catch on.  I assume you're suggesting calling
> nested_vmx_updated_pending_dbg() so that the pending #DB naturally gets
> propagated to/from vmcs12 on SMI/RSM?  I think that should work.

This works for L2, but not L1 :-(  And L2 can't be fixed without first
fixing L1 because inject_pending_event() also incorrectly prioritizes #DB
over SMI.  For L1, utilizing SMRAM to save/restore the pending #DB is
likely the easiest solution as it avoids having to add new state for
migration.

I have everything coded up but it'll probably take a few weeks to test and
get it sent out, need to focus on other stuff for a while.

  reply	other threads:[~2020-04-29 20:06 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-23  2:25 [PATCH 00/13] KVM: x86: Event fixes and cleanup Sean Christopherson
2020-04-23  2:25 ` [PATCH 01/13] KVM: nVMX: Preserve exception priority irrespective of exiting behavior Sean Christopherson
2020-04-28 18:54   ` Jim Mattson
2020-04-28 20:07     ` Oliver Upton
2020-04-23  2:25 ` [PATCH 02/13] KVM: nVMX: Open a window for pending nested VMX preemption timer Sean Christopherson
2020-04-28 21:39   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 03/13] KVM: x86: Set KVM_REQ_EVENT if run is canceled with req_immediate_exit set Sean Christopherson
2020-04-28 21:41   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 04/13] KVM: x86: Make return for {interrupt_nmi}_allowed() a bool instead of int Sean Christopherson
2020-04-28 21:42   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 05/13] KVM: nVMX: Move nested_exit_on_nmi() to nested.h Sean Christopherson
2020-04-28 21:44   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 06/13] KVM: nVMX: Report NMIs as allowed when in L2 and Exit-on-NMI is set Sean Christopherson
2020-04-28 21:46   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 07/13] KVM: VMX: Split out architectural interrupt/NMI blocking checks Sean Christopherson
2020-04-28 21:57   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 08/13] KVM: nVMX: Preserve IRQ/NMI priority irrespective of exiting behavior Sean Christopherson
2020-04-28 21:58   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 09/13] KVM: nVMX: Prioritize SMI over nested IRQ/NMI Sean Christopherson
2020-04-28 22:04   ` Jim Mattson
2020-04-28 22:59     ` Sean Christopherson
2020-04-28 23:16       ` Jim Mattson
2020-04-29 14:50         ` Sean Christopherson
2020-04-29 20:06           ` Sean Christopherson [this message]
2020-04-28 23:23       ` Jim Mattson
2020-04-23  2:25 ` [PATCH 10/13] KVM: x86: WARN on injected+pending exception even in nested case Sean Christopherson
2020-04-28 22:05   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 11/13] KVM: VMX: Use vmx_interrupt_blocked() directly from vmx_handle_exit() Sean Christopherson
2020-04-28 22:07   ` Jim Mattson
2020-04-23  2:25 ` [PATCH 12/13] KVM: x86: Replace late check_nested_events() hack with more precise fix Sean Christopherson
2020-04-23 11:00   ` Paolo Bonzini
2020-04-28 22:12   ` Jim Mattson
2020-04-28 22:20     ` Sean Christopherson
2020-04-29  8:36       ` Paolo Bonzini
2020-04-29 16:45         ` Sean Christopherson
2020-04-29 16:58           ` Paolo Bonzini
2020-04-29 17:07             ` Sean Christopherson
2020-04-23  2:25 ` [PATCH 13/13] KVM: VMX: Use vmx_get_rflags() to query RFLAGS in vmx_interrupt_blocked() Sean Christopherson
2020-04-28 22:13   ` Jim Mattson

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