linux-kernel - Re: [PATCH RESEND] KVM: X86: Use IPI shorthands in kvm guest when support

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Date:   Tue, 30 Jul 2019 10:17:58 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nadav Amit <namit@...are.com>
Subject: Re: [PATCH RESEND] KVM: X86: Use IPI shorthands in kvm guest when support

On Tue, 30 Jul 2019 at 01:50, Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Fri, Jul 26, 2019 at 02:15:27PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > IPI shorthand is supported now by linux apic/x2apic driver, switch to
> > IPI shorthand for all excluding self and all including self destination
> > shorthand in kvm guest, to avoid splitting the target mask into serveral
> > PV IPI hypercalls.
> >
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> > Cc: Nadav Amit <namit@...are.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> > Note: rebase against tip tree's x86/apic branch
> >
> >  arch/x86/kernel/kvm.c | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> > index b7f34fe..87b73b8 100644
> > --- a/arch/x86/kernel/kvm.c
> > +++ b/arch/x86/kernel/kvm.c
> > @@ -34,7 +34,9 @@
> >  #include <asm/hypervisor.h>
> >  #include <asm/tlb.h>
> >
> > +static struct apic orig_apic;
>
> Copying the entire struct apic to snapshot two functions is funky,
> explicitly capturing the two functions would be more intuitive.
>
> Tangentially related, kvm_setup_pv_ipi() can be annotated __init,
> which means the function snapshots can be __ro_after_init.
>
> That being said, can't we just remove kvm_send_ipi_all() and
> kvm_send_ipi_allbutself()?  AFAICT, the variations that lead to shorthand
> are only used when apic_use_ipi_shorthand is true.  If that isn't the
> case, fixing the callers in the APIC code seems like the correct thing to
> do.

The callers in the APIC codes have already done this, so I just remove
the two hooks in v2.

Regards,
Wanpeng Li