On Thu, Sep 12 2024, Ganapatrao Kulkarni <gankulka...@os.amperecomputing.com>
wrote:
> Extend the 'mte' property for the virt machine to cover KVM as
> well. For KVM, we don't allocate tag memory, but instead enable
> the capability.
>
> If MTE has been enabled, we need to disable migration, as we do not
> yet have a way to migrate the tags as well. Therefore, MTE will stay
> off with KVM unless requested explicitly.
>
> This patch is rework of commit b320e21c48ce64853904bea6631c0158cc2ef227
> which broke TCG since it made the TCG -cpu max
> report the presence of MTE to the guest even if the board hadn't
> enabled MTE by wiring up the tag RAM. This meant that if the guest
> then tried to use MTE QEMU would segfault accessing the
> non-existent tag RAM.
>
> Signed-off-by: Cornelia Huck <coh...@redhat.com>
> Signed-off-by: Ganapatrao Kulkarni <gankulka...@os.amperecomputing.com>
> ---
> Changes since V1:
> Added code to enable MTE before reading register
> id_aa64pfr1 (unmasked MTE bits).
>
> This patch is boot tested on ARM64 with KVM and on X86 with TCG for mte=on
> and default case(i.e, no mte).
>
> hw/arm/virt.c | 72 ++++++++++++++++++++++++++------------------
> target/arm/cpu.c | 7 +++--
> target/arm/cpu.h | 2 ++
> target/arm/kvm.c | 59 ++++++++++++++++++++++++++++++++++++
> target/arm/kvm_arm.h | 19 ++++++++++++
> 5 files changed, 126 insertions(+), 33 deletions(-)
>
(...)
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 849e2e21b3..29865609fb 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -39,6 +39,7 @@
> #include "hw/acpi/acpi.h"
> #include "hw/acpi/ghes.h"
> #include "target/arm/gtimer.h"
> +#include "migration/blocker.h"
>
> const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
> KVM_CAP_LAST_INFO
> @@ -119,6 +120,21 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t
> *cpus_to_try,
> if (vmfd < 0) {
> goto err;
> }
> +
> + /*
> + * MTE bits of register id_aa64pfr1 are masked if MTE is
> + * not enabled and required to enable before VCPU
> + * is created. Hence enable MTE(if supported) before VCPU
> + * is created to read unmasked MTE bits.
> + */
Maybe
"KVM will mask the MTE bits in id_aa64pfr1 unless the VMM has enabled
the MTE KVM capability, so do it here for probing."
?
> + if (kvm_arm_mte_supported()) {
> + KVMState kvm_state;
> +
> + kvm_state.fd = kvmfd;
> + kvm_state.vmfd = vmfd;
> + kvm_vm_enable_cap(&kvm_state, KVM_CAP_ARM_MTE, 0);
> + }
> +
> cpufd = ioctl(vmfd, KVM_CREATE_VCPU, 0);
> if (cpufd < 0) {
> goto err;
