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Re: [Qemu-ppc] [RFC PATCH v4 2/5] kvm-all: Introduce kvm_set_singlestep
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [RFC PATCH v4 2/5] kvm-all: Introduce kvm_set_singlestep |
Date: |
Wed, 13 Mar 2019 15:25:16 +1100 |
User-agent: |
Mutt/1.11.3 (2019-02-01) |
On Fri, Mar 08, 2019 at 04:09:56PM -0300, Fabiano Rosas wrote:
> David Gibson <address@hidden> writes:
>
> >> +/* Whether the KVM_SET_GUEST_DEBUG ioctl supports single stepping */
> >> +int kvm_has_guestdbg_singlestep(void)
> >> +{
> >> + /* return kvm_check_extension(kvm_state, KVM_CAP_GUEST_DEBUG_SSTEP);
> >> */
> >
> > I don't see a KVM_CAP_GUEST_DEBUG_SSTEP in either the qemu or kernel
> > trees. Where does that come from?
> >
>
> I realized that this will cause a regression for the other architectures
> (and even PPC-PR) that already have the feature when we run QEMU on
> older kernels without this capability.
>
> I am becoming inclined to rely on kvmppc_is_pr. Do you see another way
> around this?
It's ok to use that for fallback cases. However it's best if you can
design things so that modern kernels will provide a clear answer via
the CAP, either positive or negative, and only fallback to
kvmppc_is_pr() in the case where it's an old kernel.
That obviously also won't cover the other arch case.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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