linux-kernel - Re: [PATCH] PPC: KVM: fix VCPU run for HV KVM

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Message-Id: <D4E5BCE4-99BA-40B3-8726-71E71168FC54@suse.de>
Date:	Tue, 4 Feb 2014 09:09:44 +0100
From:	Alexander Graf <agraf@...e.de>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org, Paul Mackerras <paulus@...ba.org>,
	kvm-ppc <kvm-ppc@...r.kernel.org>,
	"kvm@...r.kernel.org mailing list" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PPC: KVM: fix VCPU run for HV KVM


On 04.02.2014, at 09:03, Alexey Kardashevskiy <aik@...abs.ru> wrote:

> On 01/13/2014 02:44 AM, Alexander Graf wrote:
>> 
>> On 10.01.2014, at 08:21, Alexey Kardashevskiy <aik@...abs.ru> wrote:
>> 
>>> When write to MMIO happens and there is an ioeventfd for that and
>>> is handled successfully, ioeventfd_write() returns 0 (success) and
>>> kvmppc_handle_store() returns EMULATE_DONE. Then kvmppc_emulate_mmio()
>>> converts EMULATE_DONE to RESUME_GUEST_NV and this broke from the loop.
>>> 
>>> This adds handling of RESUME_GUEST_NV in kvmppc_vcpu_run_hv().
>>> 
>>> Cc: Michael S. Tsirkin <mst@...hat.com>
>>> Suggested-by: Paul Mackerras <paulus@...ba.org>
>>> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
>>> ---
>>> 
>>> This definitely needs a better commit message. Please, help.
>>> ps. it seems like ioeventfd never worked on ppc64. hm.
>>> 
>>> ---
>>> arch/powerpc/kvm/book3s_hv.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>>> index 072287f..24f363f 100644
>>> --- a/arch/powerpc/kvm/book3s_hv.c
>>> +++ b/arch/powerpc/kvm/book3s_hv.c
>>> @@ -1569,7 +1569,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
>>> 				vcpu->arch.fault_dar, vcpu->arch.fault_dsisr);
>>> 			srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx);
>>> 		}
>>> -	} while (r == RESUME_GUEST);
>>> +	} while ((r == RESUME_GUEST_NV) || (r == RESUME_GUEST));
>> 
>> How about
>> 
>>  while(!(r & RESUME_FLAG_HOST));
> 
> 
> Rather "while(!(r & RESUME_FLAG_HOST) && (r > 0));" and still not obvious
> that this is really better.
> 
> Paul agrees with the original patch (and made a better commit message for
> our internal tree) but I just cannot make him reply in this thread, keep
> constantly asking him but to no avail :)
> 
> 
>> That should cover all RESUME_GUEST_XXX cases just fine. Apart from that
>> I agree that we should check for ! FLAG_HOST bit rather than the actual
>> RESUME_GUEST value in all case where we check for it (read: please
>> update all places).
> 
> There are 3 places remotely similar to this and none of them requires a fix
> like above.

Not today. Then someone goes in and realizes that CEDE advanced version 8 should clear r15 at which point you have to set RESUME_GUEST_NV and are in the same mess again. Let's just always treat RESUME_GUEST_NV and RESUME_GUEST as identical when checking for it.

If you like, add a small helper like

static inline bool is_resume_guest(int r) {
  return (r == RESUME_GUEST || r == RESUME_GUEST_NV);
}

in a header and use that one instead. That way we're guaranteed to be consistent.


Alex

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