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From: | Ying Fang |
Subject: | Re: [RFC PATCH 02/12] target/arm/kvm64: make MPIDR consistent with CPU Topology |
Date: | Thu, 17 Sep 2020 21:19:34 +0800 |
User-agent: | Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
On 9/17/2020 6:59 PM, Andrew Jones wrote:
On Thu, Sep 17, 2020 at 09:53:35AM +0200, Andrew Jones wrote:On Thu, Sep 17, 2020 at 11:20:23AM +0800, Ying Fang wrote:MPIDR helps to provide an additional PE identification in a multiprocessor system. This patch adds support for setting MPIDR from userspace, so that MPIDR is consistent with CPU topology configured. Signed-off-by: Ying Fang <fangying1@huawei.com> --- target/arm/kvm64.c | 46 ++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 38 insertions(+), 8 deletions(-) diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c index ef1e960285..fcce261a10 100644 --- a/target/arm/kvm64.c +++ b/target/arm/kvm64.c @@ -757,10 +757,46 @@ static int kvm_arm_sve_set_vls(CPUState *cs)#define ARM_CPU_ID_MPIDR 3, 0, 0, 0, 5 +static int kvm_arm_set_mp_affinity(CPUState *cs)+{ + uint64_t mpidr; + ARMCPU *cpu = ARM_CPU(cs); + + if (kvm_check_extension(kvm_state, KVM_CAP_ARM_MP_AFFINITY)) { + /* Make MPIDR consistent with CPU topology */ + MachineState *ms = MACHINE(qdev_get_machine()); + + mpidr = (kvm_arch_vcpu_id(cs) % ms->smp.threads) << ARM_AFF0_SHIFT;We should query KVM first to determine if it wants guests to see their PEs as threads or not. If not, and ms->smp.threads is > 1, then that's an error. And, in any case, if ms->smp.threads == 1, then we shouldn't waste aff0 on it, as that could reduce IPI broadcast performance.+ mpidr |= ((kvm_arch_vcpu_id(cs) / ms->smp.threads % ms->smp.cores) + & 0xff) << ARM_AFF1_SHIFT; + mpidr |= (kvm_arch_vcpu_id(cs) / (ms->smp.cores * ms->smp.threads) + & 0xff) << ARM_AFF2_SHIFT;Also, as pointed out in the KVM thread, we should not be attempting to describe topology with the MPIDR at all. Alexandru pointed out [*] as evidence for that. However, we do need to consider the limits on Aff0 imposed by the GIC. See hw/arm/virt.c:virt_cpu_mp_affinity() for how we currently do it for TCG. We should do something similar for KVM guests when we're taking full control of the MPIDR. [*] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=3102bc0e6ac7 Thanks, drew
Thanks for your information on MPIDR. As described in [*], MPIDR cannot be trusted as the actual topology. After applying: arm64: topology: Stop using MPIDR for topology informationCan we just use topology information from ACPI or fdt as topology and ignore MPIDR ?
+ + /* Override mp affinity when KVM is in use */ + cpu->mp_affinity = mpidr & ARM64_AFFINITY_MASK; + + /* Bit 31 is RES1 indicates the ARMv7 Multiprocessing Extensions */ + mpidr |= (1ULL << 31); + return kvm_vcpu_ioctl(cs, KVM_ARM_SET_MP_AFFINITY, &mpidr); + } else { + /* + * When KVM_CAP_ARM_MP_AFFINITY is not supported, it means KVM has its + * own idea about MPIDR assignment, so we override our defaults with + * what we get from KVM. + */ + int ret = kvm_get_one_reg(cs, ARM64_SYS_REG(ARM_CPU_ID_MPIDR), &mpidr); + if (ret) { + error_report("failed to set MPIDR");We don't need this error, kvm_get_one_reg() has trace support already. Anyway, the wording is wrong since it says 'set' instead of 'get'.+ return ret; + } + cpu->mp_affinity = mpidr & ARM32_AFFINITY_MASK; + return ret; + } +} + int kvm_arch_init_vcpu(CPUState *cs) { int ret; - uint64_t mpidr; ARMCPU *cpu = ARM_CPU(cs); CPUARMState *env = &cpu->env;@@ -814,16 +850,10 @@ int kvm_arch_init_vcpu(CPUState *cs)} }- /*- * When KVM is in use, PSCI is emulated in-kernel and not by qemu. - * Currently KVM has its own idea about MPIDR assignment, so we - * override our defaults with what we get from KVM. - */ - ret = kvm_get_one_reg(cs, ARM64_SYS_REG(ARM_CPU_ID_MPIDR), &mpidr); + ret = kvm_arm_set_mp_affinity(cs); if (ret) { return ret; } - cpu->mp_affinity = mpidr & ARM64_AFFINITY_MASK;kvm_arm_init_debug(cs); --2.23.0Thanks, drew.
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