On Mon, Dec 11, 2017 at 02:12:41PM +0100, Cornelia Huck wrote:
> On Mon, 4 Dec 2017 21:35:36 +0100
> Christoffer Dall <cdall@kernel.org> wrote:
>
> > From: Christoffer Dall <christoffer.dall@linaro.org>
> >
> > Move the calls to vcpu_load() and vcpu_put() in to the architecture
> > specific implementations of kvm_arch_vcpu_ioctl() which dispatches
> > further architecture-specific ioctls on to other functions.
> >
> > Some architectures support asynchronous vcpu ioctls which cannot call
> > vcpu_load() or take the vcpu->mutex, because that would prevent
> > concurrent execution with a running VCPU, which is the intended purpose
> > of these ioctls, for example because they inject interrupts.
> >
> > We repeat the separate checks for these specifics in the architecture
> > code for MIPS, S390 and PPC, and avoid taking the vcpu->mutex and
> > calling vcpu_load for these ioctls.
> >
> > Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> > ---
> > arch/mips/kvm/mips.c | 49 +++++++++++++++++++++++----------------
> > arch/powerpc/kvm/powerpc.c | 13 ++++++-----
> > arch/s390/kvm/kvm-s390.c | 19 ++++++++-------
> > arch/x86/kvm/x86.c | 22 +++++++++++++-----
> > virt/kvm/arm/arm.c | 58
> > ++++++++++++++++++++++++++++++++--------------
> > virt/kvm/kvm_main.c | 2 --
> > 6 files changed, 103 insertions(+), 60 deletions(-)
> >
> > diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> > index 3a898712d6cd..4a039341dc29 100644
> > --- a/arch/mips/kvm/mips.c
> > +++ b/arch/mips/kvm/mips.c
> > @@ -913,56 +913,65 @@ long kvm_arch_vcpu_ioctl(struct file *filp, unsigned
> > int ioctl,
> > void __user *argp = (void __user *)arg;
> > long r;
> >
> > + if (ioctl == KVM_INTERRUPT) {
>
> I would add a comment here that this ioctl is async to vcpu execution,
> so it is understandable why you skip the vcpu_load().
Yes, that would be appropriate.
>
> [As an aside, it is nice that this is now more obvious when looking at
> the architectures' handlers.]
>
Agreed.
> > + struct kvm_mips_interrupt irq;
> > +
> > + if (copy_from_user(&irq, argp, sizeof(irq)))
> > + return -EFAULT;
> > + kvm_debug("[%d] %s: irq: %d\n", vcpu->vcpu_id, __func__,
> > + irq.irq);
> > +
> > + return kvm_vcpu_ioctl_interrupt(vcpu, &irq);
> > + }
> > +
> > + vcpu_load(vcpu);
> > +
> > switch (ioctl) {
>
> (...)
>
> > diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> > index c06bc9552438..6b5dd3a25fe8 100644
> > --- a/arch/powerpc/kvm/powerpc.c
> > +++ b/arch/powerpc/kvm/powerpc.c
> > @@ -1617,16 +1617,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> > void __user *argp = (void __user *)arg;
> > long r;
> >
> > - switch (ioctl) {
> > - case KVM_INTERRUPT: {
> > + if (ioctl == KVM_INTERRUPT) {
>
> Same here.
>
> > struct kvm_interrupt irq;
> > - r = -EFAULT;
> > if (copy_from_user(&irq, argp, sizeof(irq)))
> > - goto out;
> > - r = kvm_vcpu_ioctl_interrupt(vcpu, &irq);
> > - goto out;
> > + return -EFAULT;
> > + return kvm_vcpu_ioctl_interrupt(vcpu, &irq);
> > }
> >
> > + vcpu_load(vcpu);
> > +
> > + switch (ioctl) {
> > case KVM_ENABLE_CAP:
> > {
> > struct kvm_enable_cap cap;
> > @@ -1666,6 +1666,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> > }
> >
> > out:
> > + vcpu_put(vcpu);
> > return r;
> > }
> >
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index 43278f334ce3..cd067b63d77f 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -3743,24 +3743,25 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> > case KVM_S390_IRQ: {
> > struct kvm_s390_irq s390irq;
> >
> > - r = -EFAULT;
> > if (copy_from_user(&s390irq, argp, sizeof(s390irq)))
> > - break;
> > - r = kvm_s390_inject_vcpu(vcpu, &s390irq);
> > - break;
> > + return -EFAULT;
> > + return kvm_s390_inject_vcpu(vcpu, &s390irq);
> > }
> > case KVM_S390_INTERRUPT: {
> > struct kvm_s390_interrupt s390int;
> > struct kvm_s390_irq s390irq;
> >
> > - r = -EFAULT;
> > if (copy_from_user(&s390int, argp, sizeof(s390int)))
> > - break;
> > + return -EFAULT;
> > if (s390int_to_s390irq(&s390int, &s390irq))
> > return -EINVAL;
> > - r = kvm_s390_inject_vcpu(vcpu, &s390irq);
> > - break;
> > + return kvm_s390_inject_vcpu(vcpu, &s390irq);
> > }
> > + }
>
> I find the special casing with the immediate return a bit ugly. Maybe
> introduce a helper async_vcpu_ioctl() or so that sets -ENOIOCTLCMD in
> its default case and return here if ret != -ENOIOCTLCMD? Christian,
> what do you think?
>
> > +
> > + vcpu_load(vcpu);
> > +
> > + switch (ioctl) {
> > case KVM_S390_STORE_STATUS:
> > idx = srcu_read_lock(&vcpu->kvm->srcu);
> > r = kvm_s390_vcpu_store_status(vcpu, arg);
> > @@ -3883,6 +3884,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> > default:
> > r = -ENOTTY;
> > }
> > +
> > + vcpu_put(vcpu);
> > return r;
> > }
> >
>
> (...)
>
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 06751bbecd58..ad5f83159a15 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2693,9 +2693,7 @@ static long kvm_vcpu_ioctl(struct file *filp,
> > break;
> > }
> > default:
> > - vcpu_load(vcpu);
> > r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
> > - vcpu_put(vcpu);
> > }
> > out:
> > mutex_unlock(&vcpu->mutex);
>
> It would be nice if we could get rid of the special casing at the
> beginning of this function, but as it would involve not taking the
> mutex for special cases (and not releasing it for those special cases),
> I don't see an elegant way to do that.
I would also have liked that, and that's essentially what I had in the
first version, but Paolo thought the result was too high an increase in
complexity in the architecture-specfic functions throughout. I don't
have any better suggestions either.
Thanks,
-Christoffer
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