From: Andrea Arcangeli <aarcange@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Peter Xu <peterx@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers
Date: Mon, 23 Sep 2019 15:05:14 -0400 [thread overview]
Message-ID: <20190923190514.GB19996@redhat.com> (raw)
In-Reply-To: <7329012d-0b3b-ce86-f58d-3d2d5dc5a790@redhat.com>
On Mon, Sep 23, 2019 at 11:57:57AM +0200, Paolo Bonzini wrote:
> On 23/09/19 11:31, Vitaly Kuznetsov wrote:
> > +#ifdef CONFIG_RETPOLINE
> > + if (exit_reason == EXIT_REASON_MSR_WRITE)
> > + return handle_wrmsr(vcpu);
> > + else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
> > + return handle_preemption_timer(vcpu);
> > + else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT)
> > + return handle_interrupt_window(vcpu);
> > + else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
> > + return handle_external_interrupt(vcpu);
> > + else if (exit_reason == EXIT_REASON_HLT)
> > + return handle_halt(vcpu);
> > + else if (exit_reason == EXIT_REASON_PAUSE_INSTRUCTION)
> > + return handle_pause(vcpu);
> > + else if (exit_reason == EXIT_REASON_MSR_READ)
> > + return handle_rdmsr(vcpu);
> > + else if (exit_reason == EXIT_REASON_CPUID)
> > + return handle_cpuid(vcpu);
> > + else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
> > + return handle_ept_misconfig(vcpu);
> > +#endif
> > return kvm_vmx_exit_handlers[exit_reason](vcpu);
>
> Most of these, while frequent, are already part of slow paths.
>
> I would keep only EXIT_REASON_MSR_WRITE, EXIT_REASON_PREEMPTION_TIMER,
> EXIT_REASON_EPT_MISCONFIG and add EXIT_REASON_IO_INSTRUCTION.
Intuition doesn't work great when it comes to CPU speculative
execution runtime. I can however run additional benchmarks to verify
your theory that keeping around frequent retpolines will still perform
ok.
> If you make kvm_vmx_exit_handlers const, can the compiler substitute for
> instance kvm_vmx_exit_handlers[EXIT_REASON_MSR_WRITE] with handle_wrmsr?
> Just thinking out loud, not sure if it's an improvement code-wise.
gcc gets right if you make it const, it calls kvm_emulate_wrmsr in
fact. However I don't think const will fly
with_vmx_hardware_setup()... in fact at runtime testing nested I just
got:
BUG: unable to handle page fault for address: ffffffffa00751e0
#PF: supervisor write access in kernel mode
#PF: error_code(0x0003) - permissions violation
PGD 2424067 P4D 2424067 PUD 2425063 PMD 7cc09067 PTE 80000000741cb161
Oops: 0003 [#1] SMP NOPTI
CPU: 1 PID: 4458 Comm: insmod Not tainted 5.3.0+ #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS ?-20190711_202441-buildvm-armv7-10.arm.fedoraproject.or4
RIP: 0010:nested_vmx_hardware_setup+0x29a/0x37a [kvm_intel]
Code: 41 ff c5 66 89 2c 85 20 92 0b a0 66 44 89 34 85 22 92 0b a0 49 ff c7 e9 e6 fe ff ff 44 89 2d 28 24 fc ff 48
RSP: 0018:ffffc90000257c18 EFLAGS: 00010246
RAX: ffffffffa001e0b0 RBX: ffffffffa0075140 RCX: 0000000000000000
RDX: ffff888078f60000 RSI: 0000000000002401 RDI: 0000000000000018
RBP: 0000000000006c08 R08: 0000000000001000 R09: 000000000007ffdc
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000006c08
R13: 0000000000000017 R14: 0000000000000268 R15: 0000000000000018
FS: 00007f7fb7ef0b80(0000) GS:ffff88807da40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffa00751e0 CR3: 0000000079620001 CR4: 0000000000160ee0
Call Trace:
hardware_setup+0x4df/0x5b2 [kvm_intel]
kvm_arch_hardware_setup+0x2f/0x27b [kvm_intel]
kvm_init+0x5d/0x26d [kvm_intel]
next prev parent reply other threads:[~2019-09-23 19:05 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-20 21:24 [PATCH 00/17] KVM monolithic v1 Andrea Arcangeli
2019-09-20 21:24 ` [PATCH 01/17] x86: spec_ctrl: fix SPEC_CTRL initialization after kexec Andrea Arcangeli
2019-09-23 10:22 ` Paolo Bonzini
2019-09-23 15:30 ` Sean Christopherson
2019-09-23 17:34 ` Andrea Arcangeli
2019-09-23 22:27 ` Sean Christopherson
2019-09-20 21:24 ` [PATCH 02/17] KVM: monolithic: x86: convert the kvm_x86_ops methods to external functions Andrea Arcangeli
2019-09-23 10:19 ` Paolo Bonzini
2019-09-23 16:13 ` Sean Christopherson
2019-09-23 16:51 ` Paolo Bonzini
2019-09-23 19:21 ` Andrea Arcangeli
2019-09-20 21:24 ` [PATCH 03/17] KVM: monolithic: x86: handle the request_immediate_exit variation Andrea Arcangeli
2019-09-23 22:35 ` Sean Christopherson
2019-09-23 23:06 ` Andrea Arcangeli
2019-09-23 23:45 ` Sean Christopherson
2019-09-24 0:24 ` Andrea Arcangeli
2019-09-20 21:24 ` [PATCH 04/17] KVM: monolithic: x86: convert the kvm_pmu_ops methods to external functions Andrea Arcangeli
2019-09-20 21:24 ` [PATCH 05/17] KVM: monolithic: x86: enable the kvm_x86_ops " Andrea Arcangeli
2019-09-20 21:24 ` [PATCH 06/17] KVM: monolithic: x86: enable the kvm_pmu_ops " Andrea Arcangeli
2019-09-20 21:24 ` [PATCH 07/17] KVM: monolithic: x86: adjust the section prefixes Andrea Arcangeli
2019-09-23 10:15 ` Paolo Bonzini
2019-09-25 12:13 ` Andrea Arcangeli
2019-09-25 12:32 ` Paolo Bonzini
2019-09-20 21:25 ` [PATCH 08/17] KVM: monolithic: adjust the section prefixes in the KVM common code Andrea Arcangeli
2019-09-20 21:25 ` [PATCH 09/17] KVM: monolithic: x86: remove kvm.ko Andrea Arcangeli
2019-09-20 21:25 ` [PATCH 10/17] KVM: monolithic: x86: use the external functions instead of kvm_x86_ops Andrea Arcangeli
2019-09-23 10:02 ` Paolo Bonzini
2019-09-20 21:25 ` [PATCH 11/17] KVM: monolithic: x86: remove exports Andrea Arcangeli
2019-09-20 21:25 ` [PATCH 12/17] KVM: monolithic: remove exports from KVM common code Andrea Arcangeli
2019-09-20 21:25 ` [PATCH 13/17] KVM: monolithic: x86: drop the kvm_pmu_ops structure Andrea Arcangeli
2019-09-23 10:21 ` Paolo Bonzini
2019-09-24 0:51 ` Andrea Arcangeli
2019-09-24 1:24 ` Paolo Bonzini
2019-09-20 21:25 ` [PATCH 14/17] KVM: monolithic: x86: inline more exit handlers in vmx.c Andrea Arcangeli
2019-09-23 10:19 ` Paolo Bonzini
2019-09-24 1:00 ` Andrea Arcangeli
2019-09-24 1:25 ` Paolo Bonzini
2019-09-24 1:55 ` Andrea Arcangeli
2019-09-24 2:56 ` Andrea Arcangeli
2019-09-25 7:52 ` Paolo Bonzini
2019-09-20 21:25 ` [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers Andrea Arcangeli
2019-09-23 9:31 ` Vitaly Kuznetsov
2019-09-23 9:57 ` Paolo Bonzini
2019-09-23 19:05 ` Andrea Arcangeli [this message]
2019-09-23 20:23 ` Sean Christopherson
2019-09-23 21:08 ` Andrea Arcangeli
2019-09-23 21:24 ` Sean Christopherson
2019-09-23 23:43 ` Andrea Arcangeli
2019-09-23 23:52 ` Sean Christopherson
2019-09-24 0:16 ` Paolo Bonzini
2019-09-24 0:35 ` Sean Christopherson
2019-09-24 0:37 ` Paolo Bonzini
2019-09-24 0:15 ` Paolo Bonzini
2019-09-24 0:38 ` Andrea Arcangeli
2019-09-24 0:46 ` Sean Christopherson
2019-09-24 21:46 ` Andrea Arcangeli
2019-09-25 7:50 ` Paolo Bonzini
2019-09-23 16:37 ` Sean Christopherson
2019-09-23 16:53 ` Paolo Bonzini
2019-09-23 17:42 ` Andrea Arcangeli
2019-09-23 18:15 ` Sean Christopherson
2019-09-23 19:12 ` Andrea Arcangeli
[not found] ` <E8FE7592-69C3-455E-8D80-A2D73BB2E14C@dinechin.org>
2019-09-25 20:51 ` Andrea Arcangeli
2019-09-23 16:28 ` Sean Christopherson
2019-09-20 21:25 ` [PATCH 16/17] KVM: retpolines: x86: eliminate retpoline from svm.c " Andrea Arcangeli
2019-09-23 10:01 ` Paolo Bonzini
2019-09-20 21:25 ` [PATCH 17/17] x86: retpolines: eliminate retpoline from msr event handlers Andrea Arcangeli
2019-09-23 15:39 ` [PATCH 00/17] KVM monolithic v1 Sean Christopherson
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