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Message-ID: <98cb06ed-acd2-a954-9c85-3c9847631106@redhat.com>
Date: Mon, 26 Jul 2021 15:32:01 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
x86@...nel.org, kvm@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 4/6] x86/kvm: introduce per cpu vcpu masks
On 01/07/21 17:41, Juergen Gross wrote:
> In order to support high vcpu numbers per guest don't use on stack
> vcpu bitmasks. As all those currently used bitmasks are not used in
> functions subject to recursion it is fairly easy to replace them with
> percpu bitmasks.
>
> Disable preemption while such a bitmask is being used in order to
> avoid double usage in case we'd switch cpus.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
Please use a local_lock instead of disabling preemption.
Paolo
> ---
> arch/x86/include/asm/kvm_host.h | 7 +++++++
> arch/x86/kvm/hyperv.c | 25 ++++++++++++++++++-------
> arch/x86/kvm/irq_comm.c | 9 +++++++--
> arch/x86/kvm/x86.c | 20 +++++++++++++++++++-
> 4 files changed, 51 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 88b1ff898fb9..79138c91f83d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1514,6 +1514,13 @@ extern u64 kvm_default_tsc_scaling_ratio;
> extern bool kvm_has_bus_lock_exit;
> /* maximum vcpu-id */
> extern unsigned int max_vcpu_id;
> +/* per cpu vcpu bitmasks (disable preemption during usage) */
> +extern unsigned long __percpu *kvm_pcpu_vcpu_mask;
> +#define KVM_VCPU_MASK_SZ \
> + (sizeof(*kvm_pcpu_vcpu_mask) * BITS_TO_LONGS(KVM_MAX_VCPUS))
> +extern u64 __percpu *kvm_hv_vp_bitmap;
> +#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64)
> +#define KVM_HV_VPMAP_SZ (sizeof(u64) * KVM_HV_MAX_SPARSE_VCPU_SET_BITS)
>
> extern u64 kvm_mce_cap_supported;
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index f00830e5202f..32d31a7334fa 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -40,7 +40,7 @@
> /* "Hv#1" signature */
> #define HYPERV_CPUID_SIGNATURE_EAX 0x31237648
>
> -#define KVM_HV_MAX_SPARSE_VCPU_SET_BITS DIV_ROUND_UP(KVM_MAX_VCPUS, 64)
> +u64 __percpu *kvm_hv_vp_bitmap;
>
> static void stimer_mark_pending(struct kvm_vcpu_hv_stimer *stimer,
> bool vcpu_kick);
> @@ -1612,8 +1612,7 @@ static __always_inline unsigned long *sparse_set_to_vcpu_mask(
> struct kvm_vcpu *vcpu;
> int i, bank, sbank = 0;
>
> - memset(vp_bitmap, 0,
> - KVM_HV_MAX_SPARSE_VCPU_SET_BITS * sizeof(*vp_bitmap));
> + memset(vp_bitmap, 0, KVM_HV_VPMAP_SZ);
> for_each_set_bit(bank, (unsigned long *)&valid_bank_mask,
> KVM_HV_MAX_SPARSE_VCPU_SET_BITS)
> vp_bitmap[bank] = sparse_banks[sbank++];
> @@ -1637,8 +1636,8 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
> struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
> struct hv_tlb_flush_ex flush_ex;
> struct hv_tlb_flush flush;
> - u64 vp_bitmap[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
> - DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
> + u64 *vp_bitmap;
> + unsigned long *vcpu_bitmap;
> unsigned long *vcpu_mask;
> u64 valid_bank_mask;
> u64 sparse_banks[64];
> @@ -1696,6 +1695,10 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
>
> cpumask_clear(&hv_vcpu->tlb_flush);
>
> + preempt_disable();
> + vcpu_bitmap = this_cpu_ptr(kvm_pcpu_vcpu_mask);
> + vp_bitmap = this_cpu_ptr(kvm_hv_vp_bitmap);
> +
> vcpu_mask = all_cpus ? NULL :
> sparse_set_to_vcpu_mask(kvm, sparse_banks, valid_bank_mask,
> vp_bitmap, vcpu_bitmap);
> @@ -1707,6 +1710,8 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, u64 ingpa, u16 rep_cnt, bool
> kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH,
> NULL, vcpu_mask, &hv_vcpu->tlb_flush);
>
> + preempt_enable();
> +
> ret_success:
> /* We always do full TLB flush, set rep_done = rep_cnt. */
> return (u64)HV_STATUS_SUCCESS |
> @@ -1738,8 +1743,8 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, u64 ingpa, u64 outgpa,
> struct kvm *kvm = vcpu->kvm;
> struct hv_send_ipi_ex send_ipi_ex;
> struct hv_send_ipi send_ipi;
> - u64 vp_bitmap[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
> - DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
> + u64 *vp_bitmap;
> + unsigned long *vcpu_bitmap;
> unsigned long *vcpu_mask;
> unsigned long valid_bank_mask;
> u64 sparse_banks[64];
> @@ -1796,12 +1801,18 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, u64 ingpa, u64 outgpa,
> if ((vector < HV_IPI_LOW_VECTOR) || (vector > HV_IPI_HIGH_VECTOR))
> return HV_STATUS_INVALID_HYPERCALL_INPUT;
>
> + preempt_disable();
> + vcpu_bitmap = this_cpu_ptr(kvm_pcpu_vcpu_mask);
> + vp_bitmap = this_cpu_ptr(kvm_hv_vp_bitmap);
> +
> vcpu_mask = all_cpus ? NULL :
> sparse_set_to_vcpu_mask(kvm, sparse_banks, valid_bank_mask,
> vp_bitmap, vcpu_bitmap);
>
> kvm_send_ipi_to_many(kvm, vector, vcpu_mask);
>
> + preempt_enable();
> +
> ret_success:
> return HV_STATUS_SUCCESS;
> }
> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index d5b72a08e566..be4424ddcd8f 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -47,7 +47,7 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
> {
> int i, r = -1;
> struct kvm_vcpu *vcpu, *lowest = NULL;
> - unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
> + unsigned long *dest_vcpu_bitmap;
> unsigned int dest_vcpus = 0;
>
> if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
> @@ -59,7 +59,10 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
> irq->delivery_mode = APIC_DM_FIXED;
> }
>
> - memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));
> + preempt_disable();
> + dest_vcpu_bitmap = this_cpu_ptr(kvm_pcpu_vcpu_mask);
> +
> + memset(dest_vcpu_bitmap, 0, KVM_VCPU_MASK_SZ);
>
> kvm_for_each_vcpu(i, vcpu, kvm) {
> if (!kvm_apic_present(vcpu))
> @@ -93,6 +96,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
> lowest = kvm_get_vcpu(kvm, idx);
> }
>
> + preempt_enable();
> +
> if (lowest)
> r = kvm_apic_set_irq(lowest, irq, dest_map);
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0390d90fd360..3af398ef1fc9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -180,6 +180,8 @@ module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR);
> unsigned int __read_mostly max_vcpu_id = KVM_DEFAULT_MAX_VCPU_ID;
> module_param(max_vcpu_id, uint, S_IRUGO);
>
> +unsigned long __percpu *kvm_pcpu_vcpu_mask;
> +
> /*
> * Restoring the host value for MSRs that are only consumed when running in
> * usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU
> @@ -10646,9 +10648,18 @@ int kvm_arch_hardware_setup(void *opaque)
> if (boot_cpu_has(X86_FEATURE_XSAVES))
> rdmsrl(MSR_IA32_XSS, host_xss);
>
> + kvm_pcpu_vcpu_mask = __alloc_percpu(KVM_VCPU_MASK_SZ,
> + sizeof(unsigned long));
> + kvm_hv_vp_bitmap = __alloc_percpu(KVM_HV_VPMAP_SZ, sizeof(u64));
> +
> + if (!kvm_pcpu_vcpu_mask || !kvm_hv_vp_bitmap) {
> + r = -ENOMEM;
> + goto err;
> + }
> +
> r = ops->hardware_setup();
> if (r != 0)
> - return r;
> + goto err;
>
> memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
> kvm_ops_static_call_update();
> @@ -10676,11 +10687,18 @@ int kvm_arch_hardware_setup(void *opaque)
>
> kvm_init_msr_list();
> return 0;
> +
> + err:
> + free_percpu(kvm_pcpu_vcpu_mask);
> + free_percpu(kvm_hv_vp_bitmap);
> + return r;
> }
>
> void kvm_arch_hardware_unsetup(void)
> {
> static_call(kvm_x86_hardware_unsetup)();
> + free_percpu(kvm_pcpu_vcpu_mask);
> + free_percpu(kvm_hv_vp_bitmap);
> }
>
> int kvm_arch_check_processor_compat(void *opaque)
>
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