Re: [PATCH 07/28] kvm tools: Move 'kvm__recommended_cpus' to

Sasha Levin
2011-12-07T08:29:24Z

On Wed, 2011-12-07 at 18:28 +1100, Matt Evans wrote:
> On 07/12/11 18:24, Alexander Graf wrote:
> >
> > On 07.12.2011, at 08:19, Matt Evans <matt@ozlabs.org> wrote:
> >
> >> On 07/12/11 17:34, Sasha Levin wrote:
> >>> On Wed, 2011-12-07 at 17:17 +1100, Matt Evans wrote:
> >>>> On 06/12/11 19:20, Sasha Levin wrote:
> >>>>> Why is it getting moved out of generic code?
> >>>>>
> >>>>> This is used to determine the maximum amount of vcpus supported by the
> >>>>> host for a single guest, and as far as I know KVM_CAP_NR_VCPUS and
> >>>>> KVM_CAP_MAX_VCPUS are not arch specific.
> >>>>
> >>>> I checked api.txt and you're right, it isn't arch-specific. I assumed it was,
> >>>> because PPC KVM doesn't support it ;-) I've dropped this patch and in its place
> >>>> implemented the api.txt suggestion of "if KVM_CAP_NR_VCPUS fails, use 4" instead
> >>>> of die(); you'll see that when I repost.
> >>>>
> >>>> This will have the effect of PPC being limited to 4 CPUs until the kernel
> >>>> supports that CAP. (I'll see about this part too.)
> >>>
> >>> I went to look at which limitation PPC places on amount of vcpus in
> >>> guest, and saw this in kvmppc_core_vcpu_create() in the book3s code:
> >>>
> >>> vcpu = kvmppc_core_vcpu_create(kvm, id);
> >>> vcpu->arch.wqp = &vcpu->wq;
> >>> if (!IS_ERR(vcpu))
> >>> kvmppc_create_vcpu_debugfs(vcpu, id);
> >>>
> >>> This is wrong, right? The VCPU is dereferenced before actually checking
> >>> that it's not an error.
> >>
> >> Yeah, that's b0rk. Alex, a patch below. :)
> >
> > Thanks :). Will apply asap but don't have a real keyboard today :).
>
> Ha! Voice control on your phone, what could go wrong?
>
> > I suppose this is stable material?
>
> Good idea, (and if we're formal,
> Signed-off-by: Matt Evans <matt@ozlabs.org>
> ). I suppose no one's seen a vcpu fail to be created, yet.

I also got another one, but it's **completely untested** (not even
compiled). Alex, Matt, any chance one of you can loan a temporary ppc
shell for the upcoming tests of KVM tool/ppc KVM?

---

From: Sasha Levin <levinsasha928@gmail.com>
Date: Wed, 7 Dec 2011 10:24:56 +0200
Subject: [PATCH] KVM: PPC: Use the vcpu kmem_cache when allocating new VCPUs

Currently the code kzalloc()s new VCPUs instead of using the kmem_cache
which is created when KVM is initialized.

Modify it to allocate VCPUs from that kmem_cache.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
arch/powerpc/kvm/book3s_hv.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 0cb137a..e309099 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -411,7 +411,7 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
goto out;

err = -ENOMEM;
- vcpu = kzalloc(sizeof(struct kvm_vcpu), GFP_KERNEL);
+ vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
if (!vcpu)
goto out;

@@ -463,7 +463,7 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
return vcpu;

free_vcpu:
- kfree(vcpu);
+ kmem_cache_free(kvm_vcpu_cache, vcpu);
out:
return ERR_PTR(err);
}
@@ -471,7 +471,7 @@ out:
void kvmppc_core_vcpu_free(struct kvm_vcpu *vcpu)
{
kvm_vcpu_uninit(vcpu);
- kfree(vcpu);
+ kmem_cache_free(kvm_vcpu_cache, vcpu);
}

static void kvmppc_set_timer(struct kvm_vcpu *vcpu)

--

Sasha.