[PATCH 09/37] KVM: arm64: Move debug dirty flag calculation out of world switch
Christoffer Dall
cdall at linaro.org
Fri Dec 1 09:25:46 PST 2017
On Tue, Nov 07, 2017 at 03:09:19PM +0100, Andrew Jones wrote:
> On Thu, Oct 12, 2017 at 12:41:13PM +0200, Christoffer Dall wrote:
> > There is no need to figure out inside the world-switch if we should
> > save/restore the debug registers or not, we can might as well do that in
> > the higher level debug setup code, making it easier to optimize down the
> > line.
> >
> > Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> > ---
> > arch/arm64/kvm/debug.c | 9 +++++++++
> > arch/arm64/kvm/hyp/debug-sr.c | 6 ------
> > 2 files changed, 9 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> > index dbadfaf..62550de19 100644
> > --- a/arch/arm64/kvm/debug.c
> > +++ b/arch/arm64/kvm/debug.c
> > @@ -193,6 +193,15 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
> > if (trap_debug)
> > vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
> >
> > + /*
> > + * If any of KDE, MDE or KVM_ARM64_DEBUG_DIRTY is set, perform
> > + * a full save/restore cycle.
>
> The commit message implies testing KVM_ARM64_DEBUG_DIRTY, but it only
> tests KDE and MDE.
>
You meant the comment, right?
> > + */
> > + if ((vcpu_sys_reg(vcpu, MDSCR_EL1) & DBG_MDSCR_KDE) ||
> > + (vcpu_sys_reg(vcpu, MDSCR_EL1) & DBG_MDSCR_MDE))
>
> nit: could also write as
>
> if (vcpu_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
>
I actually prefer it the other way, and I think the compiler will figure
out what to do in terms of efficiency.
> > + vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
> > +
>
> It looks like there's only one flag for debug_flags - this dirty flag,
> which I guess is also used to trigger trapping. So maybe this could be a
> second flag of a "lazy state" field, as I suggested earlier?
>
I'm going to leave this one for now, but we can improve that later on if
we want to save a little space in the vcpu struct, or rather if we want
to rearrange things to make frequently accessed fields fit in the same
cache line.
Thanks,
-Christoffer
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