Re: [Qemu-devel] [PATCH v4 3/3] arm: implement query-gic-capabilities

[Peter Maydell]

On 8 March 2016 at 07:36, Peter Xu <address@hidden> wrote:
> For emulated GIC capabilities, currently only gicv2 is supported. We
> need to add gicv3 in when emulated gicv3 ready. For KVM accelerated ARM
> VM, we detect the capability bits using ioctls.
>
> When probing the KVM capabilities, we cannot leverage existing helper
> functions like kvm_create_device() since QEMU might be using TCG while
> probing (actually this is the case for libvirt probing). So, one
> temporary VM is created to do the probing.
>
> Signed-off-by: Peter Xu <address@hidden>
> ---
>  target-arm/machine.c | 94 
> +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 93 insertions(+), 1 deletion(-)
>
> diff --git a/target-arm/machine.c b/target-arm/machine.c
> index 813909e..8f52f74 100644
> --- a/target-arm/machine.c
> +++ b/target-arm/machine.c
> @@ -1,3 +1,5 @@
> +#include <linux/kvm.h>

This will break compilation on non-Linux hosts; you can't include
linux headers like this.

(This is all in the wrong file anyway, machine.c is for migration.)

> +#include <sys/ioctl.h>
>  #include "qemu/osdep.h"
>  #include "hw/hw.h"
>  #include "hw/boards.h"
> @@ -347,7 +349,97 @@ const char *gicv3_class_name(void)
>      exit(1);
>  }
>
> +static GICCapability *gic_cap_new(int version)
> +{
> +    GICCapability *cap = g_new0(GICCapability, 1);
> +    cap->version = version;
> +    /* by default, support none */
> +    cap->emulated = false;
> +    cap->kernel = false;
> +    return cap;
> +}
> +
> +static GICCapabilityList *gic_cap_list_add(GICCapabilityList *head,
> +                                           GICCapability *cap)
> +{
> +    GICCapabilityList *item = g_new0(GICCapabilityList, 1);
> +    item->value = cap;
> +    item->next = head;
> +    return item;
> +}
> +
> +#ifdef CONFIG_KVM
> +/* Test whether KVM support specific device. */
> +static inline int kvm_support_device(int vmfd, uint64_t type)
> +{
> +    struct kvm_create_device create_dev = {
> +        .type = type,
> +        .fd = -1,
> +        .flags = KVM_CREATE_DEVICE_TEST,
> +    };
> +    return ioctl(vmfd, KVM_CREATE_DEVICE, &create_dev);
> +}
> +#endif

This is not ARM specific so it should go in kvm-all.c.

> +
>  GICCapabilityList *qmp_query_gic_capabilities(Error **errp)
>  {
> -    return NULL;
> +    GICCapabilityList *head = NULL;
> +    GICCapability *v2 = gic_cap_new(2), *v3 = gic_cap_new(3);
> +
> +    v2->emulated = true;
> +    /* FIXME: we'd change to true after we get emulated GICv3. */
> +    v3->emulated = false;
> +
> +#ifdef CONFIG_KVM

KVM specific code should be factored out and live in one of
the target-arm/kvm*.c files.

> +    {
> +        int kvm_fd = -1;
> +        int vmfd = -1;
> +        /*
> +         * HACK: here we create one temporary VM, do the probing,
> +         * then release it properly.
> +         */
> +        kvm_fd = qemu_open("/dev/kvm", O_RDWR);
> +        if (kvm_fd == -1) {
> +            /* KVM may not enabled on host, which is fine. */
> +            goto out;
> +        }
> +
> +        do {
> +            /* For ARM, VM type could only be zero now. */
> +            vmfd = ioctl(kvm_fd, KVM_CREATE_VM, 0);
> +        } while (vmfd == -EINTR);
> +
> +        if (vmfd < 0) {
> +            goto kvm_fd_close;
> +        }

Rather than open-coding this you might as well use
kvm_arm_creat_scratch_host_vcpu() (you don't need the vcpu fd but
it's pretty harmless to create it.)


> +
> +        if (ioctl(kvm_fd, KVM_CHECK_EXTENSION,
> +                  KVM_CAP_DEVICE_CTRL) <= 0) {
> +            /* older version of KVM possibly */
> +            goto kvm_vmfd_close;
> +        }

Do this in kvm_support_device() [mostly just to parallel how
kvm_create_device() does it.]

> +
> +        /* Test KVM GICv2 */
> +        if (kvm_support_device(vmfd, KVM_DEV_TYPE_ARM_VGIC_V2) >= 0) {
> +            v2->kernel = true;
> +        }
> +
> +        /* Test KVM GICv3 */
> +        if (kvm_support_device(vmfd, KVM_DEV_TYPE_ARM_VGIC_V3) >= 0) {
> +            v3->kernel = true;
> +        }
> +
> +kvm_vmfd_close:
> +        close(vmfd);
> +kvm_fd_close:
> +        close(kvm_fd);
> +out:
> +        ;
> +    }
> +#endif
> +
> +    head = gic_cap_list_add(head, v2);
> +    head = gic_cap_list_add(head, v3);
> +
> +    return head;
>  }
> --
> 2.4.3

thanks
-- PMM