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

On 05/28/2015 07:31 AM, Daniel P. Berrange wrote: > 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. We need this in the case you are running on an aarch64 host and have both qemu-system-arm and qemu-system-aarch64 installed. In this case, when you want to use KVM for arm32, you _have_ to use qemu-system-aarch64, qemu-system-arm does not work. What you suggest would mean that qemu-system-arm is grabbed from the caps cache. x86 doesn't have this problem because qemu-system-i386, qemu-system-x86_64 and by extension qemu-kvm can all be used to do 32-on-64 KVM.