[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <Z9h7eTs8i8TRRxqU@google.com>
Date: Mon, 17 Mar 2025 12:43:53 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Add a module param to control and enumerate
device posted IRQs
On Mon, Mar 17, 2025, Yosry Ahmed wrote:
> On Fri, Mar 14, 2025 at 07:56:15PM -0700, Sean Christopherson wrote:
> > Add a module param to allow disabling device posted interrupts without
> > having to sacrifice all of APICv/AVIC, and to also effectively enumerate
> > to userspace whether or not KVM may be utilizing device posted IRQs.
> > Disabling device posted interrupts is very desirable for testing, and can
> > even be desirable for production environments, e.g. if the host kernel
> > wants to interpose on device interrupts.
> >
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> > arch/x86/include/asm/kvm_host.h | 1 +
> > arch/x86/kvm/svm/avic.c | 3 +--
> > arch/x86/kvm/vmx/posted_intr.c | 7 +++----
> > arch/x86/kvm/x86.c | 9 ++++++++-
> > 4 files changed, 13 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index d881e7d276b1..bf11c5ee50cb 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1922,6 +1922,7 @@ struct kvm_arch_async_pf {
> > extern u32 __read_mostly kvm_nr_uret_msrs;
> > extern bool __read_mostly allow_smaller_maxphyaddr;
> > extern bool __read_mostly enable_apicv;
> > +extern bool __read_mostly enable_device_posted_irqs;
> > extern struct kvm_x86_ops kvm_x86_ops;
> >
> > #define kvm_x86_call(func) static_call(kvm_x86_##func)
> > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> > index 65fd245a9953..e0f519565393 100644
> > --- a/arch/x86/kvm/svm/avic.c
> > +++ b/arch/x86/kvm/svm/avic.c
> > @@ -898,8 +898,7 @@ int avic_pi_update_irte(struct kvm *kvm, unsigned int host_irq,
> > struct kvm_irq_routing_table *irq_rt;
> > int idx, ret = 0;
> >
> > - if (!kvm_arch_has_assigned_device(kvm) ||
> > - !irq_remapping_cap(IRQ_POSTING_CAP))
> > + if (!kvm_arch_has_assigned_device(kvm) || !enable_device_posted_irqs)
>
> This function will now also be skipped if enable_apicv is false. Is this
> always the case here for some reason? Sorry if I missed something
> obvious.
Working as intended, though I failed to document it. Hrm, but I wasn't expecting
this to be a functional change. Oh, I know what happened. I had originally
tacked this on to a big series to clean up the IRTE stuff (spoiler alert), and in
that series common code checked kvm_arch_has_irq_bypass() (which incorporates
enable_apicv) before calling pi_update_irte().
I'll prepend a patch or three to do minimal cleanup before introducing the new
module param.
> > @@ -9772,6 +9776,9 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
> > if (r != 0)
> > goto out_mmu_exit;
> >
> > + enable_device_posted_irqs = enable_device_posted_irqs && enable_apicv &&
> > + irq_remapping_cap(IRQ_POSTING_CAP);
>
> Maybe this is clearer:
>
> enable_device_posted_irqs &= enable_avivc && irq_remapping_cap(IRQ_POSTING_CAP);
I don't have a strong opinion. I went with the "self check" approach purely
because SVM does so for a few params, e.b.
nrips = nrips && boot_cpu_has(X86_FEATURE_NRIPS);
Anyone else care either way? If not, I'll go with Yosry's suggestion.
Powered by blists - more mailing lists