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Re: [libvirt] [PATCH 3/3] qemu: caps: Advertise arm 32-on-64 KVM option



On Thu, May 21, 2015 at 07:03:28PM -0400, Cole Robinson wrote:
> We need to use qemu-system-aarch64 to run armv7l KVM VMs on an aarch64
> host.
> ---
>  src/qemu/qemu_capabilities.c | 42 ++++++++++++++++++++++--------------------
>  1 file changed, 22 insertions(+), 20 deletions(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index 1e7bddb..7181865 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -723,19 +723,6 @@ virQEMUCapsFindBinaryForArch(virArch hostarch,
>      return ret;
>  }
>  
> -
> -static bool
> -virQEMUCapsIsValidForKVM(virArch hostarch,
> -                         virArch guestarch)
> -{
> -    if (hostarch == guestarch)
> -        return true;
> -    if (hostarch == VIR_ARCH_X86_64 &&
> -        guestarch == VIR_ARCH_I686)
> -        return true;
> -    return false;
> -}
> -
>  static int
>  virQEMUCapsInitGuest(virCapsPtr caps,
>                       virQEMUCapsCachePtr cache,
> @@ -747,6 +734,7 @@ virQEMUCapsInitGuest(virCapsPtr caps,
>      char *binary = NULL;
>      virQEMUCapsPtr qemubinCaps = NULL;
>      virQEMUCapsPtr kvmbinCaps = NULL;
> +    bool native_kvm, x86_32on64_kvm, arm_32on64_kvm;
>      int ret = -1;
>  
>      /* Check for existence of base emulator, or alternate base
> @@ -764,16 +752,30 @@ virQEMUCapsInitGuest(virCapsPtr caps,
>  
>      /* qemu-kvm/kvm binaries can only be used if
>       *  - host & guest arches match
> -     * Or
> -     *  - hostarch is x86_64 and guest arch is i686
> -     * The latter simply needs "-cpu qemu32"
> +     *  - hostarch is x86_64 and guest arch is i686 (needs -cpu qemu32)
> +     *  - hostarch is aarch64 and guest arch is armv7l (needs -cpu aarch64=off)
>       */
> -    if (virQEMUCapsIsValidForKVM(hostarch, guestarch)) {
> -        const char *const kvmbins[] = { "/usr/libexec/qemu-kvm", /* RHEL */
> -                                        "qemu-kvm", /* Fedora */
> -                                        "kvm" }; /* Upstream .spec */
> +    native_kvm = (hostarch == guestarch);
> +    x86_32on64_kvm = (hostarch == VIR_ARCH_X86_64 &&
> +        guestarch == VIR_ARCH_I686);
> +    arm_32on64_kvm = (hostarch == VIR_ARCH_AARCH64 &&
> +        guestarch == VIR_ARCH_ARMV7L);
> +
> +    if (native_kvm || x86_32on64_kvm || arm_32on64_kvm) {
> +        const char *kvmbins[] = {
> +            "/usr/libexec/qemu-kvm", /* RHEL */
> +            "qemu-kvm", /* Fedora */
> +            "kvm", /* Debian/Ubuntu */
> +            NULL,
> +        };
> +
> +        if (arm_32on64_kvm)
> +            kvmbins[3] = "qemu-system-aarch64";

I'm unclear why you need to be adding this. We don't need it for
the equivalent i686 with qemu-system-x86_64, as the earlier call
to virQEMUCapsFindBinaryForArch() will already return the binary
qemu-system-x86_64. IIUC, it should have returned the binary
qemu-system-aarch64 too, so this just seems to duplicate the
check for that binary.


Regards,
Daniel
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