On Tue, Sep 16, 2025 at 10:13 AM Daniel P. Berrangé <[email protected]> wrote:
> CC Paolo as maintainer > > On Wed, Sep 10, 2025 at 01:57:32PM +0200, Hector Cao wrote: > > Prior to v10.1, if requested by user, arch-capabilities is always on > > despite the fact that CPUID advertises it to be off/unvailable. > > this causes a migration issue for VMs that are run on a machine > > without arch-capabilities and expect this feature to be present > > on the destination host with QEMU 10.1. > > > > This commit add a compatibility property to restore the legacy > > behavior for all machines with version prior to 10.1 > > > > Can you add a 'Fixes: <hash>' line to refer to the orignial > commit in 10.1 that introduced the regression. > Thanks Daniel for the feedback, Since this patch is a PoC at the moment, I will submit the final one later once I have enough feedback Here is the line I will add to this patch header: Fixes: d3a2413 > > > Signed-off-by: Hector Cao <[email protected]> > > --- > > hw/core/machine.c | 1 + > > migration/migration.h | 12 ++++++++++++ > > migration/options.c | 3 +++ > > target/i386/kvm/kvm.c | 5 ++++- > > 4 files changed, 20 insertions(+), 1 deletion(-) > > > > diff --git a/hw/core/machine.c b/hw/core/machine.c > > index 38c949c4f2..8ad5d79cb3 100644 > > --- a/hw/core/machine.c > > +++ b/hw/core/machine.c > > @@ -45,6 +45,7 @@ GlobalProperty hw_compat_10_0[] = { > > { "vfio-pci", "x-migration-load-config-after-iter", "off" }, > > { "ramfb", "use-legacy-x86-rom", "true"}, > > { "vfio-pci-nohotplug", "use-legacy-x86-rom", "true" }, > > + { "migration", "arch-cap-always-on", "true" }, > > }; > > const size_t hw_compat_10_0_len = G_N_ELEMENTS(hw_compat_10_0); > > > > diff --git a/migration/migration.h b/migration/migration.h > > index 01329bf824..5124ff3636 100644 > > --- a/migration/migration.h > > +++ b/migration/migration.h > > @@ -510,6 +510,18 @@ struct MigrationState { > > bool rdma_migration; > > > > GSource *hup_source; > > + > > + /* > > + * This variable allows to keep the backward compatibility with > QEMU (<10.1) > > + * on the arch-capabilities detection. > > + * With the commit d3a2413 (since 10.1), the arch-capabilities > feature is gated > > + * with the CPUID bit (CPUID_7_0_EDX_ARCH_CAPABILITIES) instead of > being always > > + * enabled when user requests for it. this new behavior breaks > migration of VMs > > + * created and run with older QEMU on machines without > IA32_ARCH_CAPABILITIES MSR, > > + * those VMs might have arch-capabilities enabled and break when > migrating > > + * to a host with QEMU 10.1 with error : missing feature > arch-capabilities > > + */ > > + bool arch_cap_always_on; > > }; > > > > void migrate_set_state(MigrationStatus *state, MigrationStatus > old_state, > > diff --git a/migration/options.c b/migration/options.c > > index 4e923a2e07..3a80dba9c5 100644 > > --- a/migration/options.c > > +++ b/migration/options.c > > @@ -203,6 +203,9 @@ const Property migration_properties[] = { > > MIGRATION_CAPABILITY_SWITCHOVER_ACK), > > DEFINE_PROP_MIG_CAP("x-dirty-limit", > MIGRATION_CAPABILITY_DIRTY_LIMIT), > > DEFINE_PROP_MIG_CAP("mapped-ram", MIGRATION_CAPABILITY_MAPPED_RAM), > > + > > + DEFINE_PROP_BOOL("arch-cap-always-on", MigrationState, > > + arch_cap_always_on, false), > > }; > > const size_t migration_properties_count = > ARRAY_SIZE(migration_properties); > > > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > > index 306430a052..e2ec4e6de5 100644 > > --- a/target/i386/kvm/kvm.c > > +++ b/target/i386/kvm/kvm.c > > @@ -42,6 +42,7 @@ > > #include "xen-emu.h" > > #include "hyperv.h" > > #include "hyperv-proto.h" > > +#include "migration/migration.h" > > > > #include "gdbstub/enums.h" > > #include "qemu/host-utils.h" > > @@ -438,6 +439,7 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, > uint32_t function, > > uint32_t ret = 0; > > uint32_t cpuid_1_edx, unused; > > uint64_t bitmask; > > + MigrationState *ms = migrate_get_current(); > > > > cpuid = get_supported_cpuid(s); > > > > @@ -508,7 +510,8 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, > uint32_t function, > > * mcahines at all, do not show the fake ARCH_CAPABILITIES MSR > that > > * KVM sets up. > > */ > > - if (!has_msr_arch_capabs || !(edx & > CPUID_7_0_EDX_ARCH_CAPABILITIES)) { > > + if (!has_msr_arch_capabs > > + || (!(edx & CPUID_7_0_EDX_ARCH_CAPABILITIES) && > (!ms->arch_cap_always_on))) { > > ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES; > > } > > } else if (function == 7 && index == 1 && reg == R_EAX) { > > -- > > 2.45.2 > > > > > > With regards, > Daniel > -- > |: https://berrange.com -o- > https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- > https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- > https://www.instagram.com/dberrange :| > > -- Hector CAO Software Engineer – Server Team / Virtualization [email protected] https://launc <https://launchpad.net/~hectorcao>hpad.net/~hectorcao <https://launchpad.net/~hectorcao> <https://launchpad.net/~hectorcao>
