[PATCH v3 15/15] kvm/arm: Align the VMID allocation with the arm64 ASID one

From: Julien Grall
Date: Wed Jul 24 2019 - 12:26:23 EST

At the moment, the VMID algorithm will send an SGI to all the CPUs to
force an exit and then broadcast a full TLB flush and I-Cache
invalidation.

This patch re-use the new ASID allocator. The
benefits are:
- CPUs are not forced to exit at roll-over. Instead the VMID will be
marked reserved and the context will be flushed at next exit. This
will reduce the IPIs traffic.
- Context invalidation is now per-CPU rather than broadcasted.
- Catalin has a formal model of the ASID allocator.

With the new algo, the code is now adapted:
- The function __kvm_flush_vm_context() has been renamed to
__kvm_tlb_flush_local_all() and now only flushing the current CPU
context.
- The call to update_vttbr() will be done with preemption disabled
as the new algo requires to store information per-CPU.
- The TLBs associated to EL1 will be flushed when booting a CPU to
deal with stale information. This was previously done on the
allocation of the first VMID of a new generation.

The measurement was made on a Seattle based SoC (8 CPUs), with the
number of VMID limited to 4-bit. The test involves running concurrently 40
guests with 2 vCPUs. Each guest will then execute hackbench 5 times
before exiting.

The performance difference between the current algo and the new one are:
- 2.5% less exit from the guest
- 22.4% more flush, although they are now local rather than
broadcasted
- 0.11% faster (just for the record)

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

----
Looking at the __kvm_flush_vm_context, it might be possible to
reduce more the overhead by removing the I-Cache flush for other
cache than VIPT. This has been left aside for now.

Changes in v3:
- Free resource if initialization failed
- s/__kvm_flush_cpu_vmid_context/__kvm_tlb_flush_local_all/
- s/asid/id/ in kvm_vmid to avoid confusion
- Generate the VMID in kvm_get_vttbr() rather than using a
callback in the ASID allocator
- Use smp_processor_id() rather than {get, put}_cpu() as the
code should already be called from non-preemptible context
- Mention the formal model in the commit message
---
arch/arm/include/asm/kvm_asm.h | 2 +-
arch/arm/include/asm/kvm_host.h | 5 +-
arch/arm/include/asm/kvm_hyp.h | 1 +
arch/arm/include/asm/kvm_mmu.h | 3 +-
arch/arm/kvm/hyp/tlb.c | 8 +--
arch/arm64/include/asm/kvm_asid.h | 8 +++
arch/arm64/include/asm/kvm_asm.h | 2 +-
arch/arm64/include/asm/kvm_host.h | 5 +-
arch/arm64/include/asm/kvm_mmu.h | 3 +-
arch/arm64/kvm/hyp/tlb.c | 10 +--
virt/kvm/arm/arm.c | 125 ++++++++++++++------------------------
11 files changed, 70 insertions(+), 102 deletions(-)
create mode 100644 arch/arm64/include/asm/kvm_asid.h

diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
index f615830f9f57..b6342258b466 100644
--- a/arch/arm/include/asm/kvm_asm.h
+++ b/arch/arm/include/asm/kvm_asm.h
@@ -53,10 +53,10 @@ struct kvm_vcpu;
extern char __kvm_hyp_init[];
extern char __kvm_hyp_init_end[];

-extern void __kvm_flush_vm_context(void);
extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
extern void __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu);
+extern void __kvm_tlb_flush_local_all(void);

extern void __kvm_timer_set_cntvoff(u32 cntvoff_low, u32 cntvoff_high);

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 8a37c8e89777..9b534f73725f 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -49,9 +49,7 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
void kvm_reset_coprocs(struct kvm_vcpu *vcpu);

struct kvm_vmid {
- /* The VMID generation used for the virt. memory system */
- u64 vmid_gen;
- u32 vmid;
+ atomic64_t id;
};

struct kvm_arch {
@@ -257,7 +255,6 @@ unsigned long __kvm_call_hyp(void *hypfn, ...);
ret; \
})

-void force_vm_exit(const cpumask_t *mask);
int __kvm_arm_vcpu_get_events(struct kvm_vcpu *vcpu,
struct kvm_vcpu_events *events);

diff --git a/arch/arm/include/asm/kvm_hyp.h b/arch/arm/include/asm/kvm_hyp.h
index 40e9034db601..46484a516e76 100644
--- a/arch/arm/include/asm/kvm_hyp.h
+++ b/arch/arm/include/asm/kvm_hyp.h
@@ -64,6 +64,7 @@
#define TLBIALLIS __ACCESS_CP15(c8, 0, c3, 0)
#define TLBIALL __ACCESS_CP15(c8, 0, c7, 0)
#define TLBIALLNSNHIS __ACCESS_CP15(c8, 4, c3, 4)
+#define TLBIALLNSNH __ACCESS_CP15(c8, 4, c7, 4)
#define PRRR __ACCESS_CP15(c10, 0, c2, 0)
#define NMRR __ACCESS_CP15(c10, 0, c2, 1)
#define AMAIR0 __ACCESS_CP15(c10, 0, c3, 0)
diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index 0d84d50bf9ba..d7208e7b01bd 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -426,7 +426,8 @@ static __always_inline u64 kvm_get_vttbr(struct kvm *kvm)
u64 vmid_field, baddr;

baddr = kvm->arch.pgd_phys;
- vmid_field = (u64)vmid->vmid << VTTBR_VMID_SHIFT;
+ vmid_field = atomic64_read(&vmid->id) << VTTBR_VMID_SHIFT;
+ vmid_field &= VTTBR_VMID_MASK(kvm_get_vmid_bits());
return kvm_phys_to_vttbr(baddr) | vmid_field;
}

diff --git a/arch/arm/kvm/hyp/tlb.c b/arch/arm/kvm/hyp/tlb.c
index 848f27bbad9d..af0108350a35 100644
--- a/arch/arm/kvm/hyp/tlb.c
+++ b/arch/arm/kvm/hyp/tlb.c
@@ -60,9 +60,9 @@ void __hyp_text __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu)
write_sysreg(0, VTTBR);
}

-void __hyp_text __kvm_flush_vm_context(void)
+void __hyp_text __kvm_tlb_flush_local_all(void)
{
- write_sysreg(0, TLBIALLNSNHIS);
- write_sysreg(0, ICIALLUIS);
- dsb(ish);
+ write_sysreg(0, TLBIALLNSNH);
+ write_sysreg(0, ICIALLU);
+ dsb(nsh);
}
diff --git a/arch/arm64/include/asm/kvm_asid.h b/arch/arm64/include/asm/kvm_asid.h
new file mode 100644
index 000000000000..8b586e43c094
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_asid.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ARM64_KVM_ASID_H__
+#define __ARM64_KVM_ASID_H__
+
+#include <asm/asid.h>
+
+#endif /* __ARM64_KVM_ASID_H__ */
+
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 44a243754c1b..0e19e8f1283a 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -57,10 +57,10 @@ extern char __kvm_hyp_init_end[];

extern char __kvm_hyp_vector[];

-extern void __kvm_flush_vm_context(void);
extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
extern void __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu);
+extern void __kvm_tlb_flush_local_all(void);

extern void __kvm_timer_set_cntvoff(u32 cntvoff_low, u32 cntvoff_high);

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f656169db8c3..501121a82bbc 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -57,9 +57,7 @@ int kvm_arch_vm_ioctl_check_extension(struct kvm *kvm, long ext);
void __extended_idmap_trampoline(phys_addr_t boot_pgd, phys_addr_t idmap_start);

struct kvm_vmid {
- /* The VMID generation used for the virt. memory system */
- u64 vmid_gen;
- u32 vmid;
+ atomic64_t id;
};

struct kvm_arch {
@@ -467,7 +465,6 @@ u64 __kvm_call_hyp(void *hypfn, ...);
ret; \
})

-void force_vm_exit(const cpumask_t *mask);
void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);

int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 2ce8055a84b8..0c5b36af4abe 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -597,7 +597,8 @@ static __always_inline u64 kvm_get_vttbr(struct kvm *kvm)
u64 cnp = system_supports_cnp() ? VTTBR_CNP_BIT : 0;

baddr = kvm->arch.pgd_phys;
- vmid_field = (u64)vmid->vmid << VTTBR_VMID_SHIFT;
+ vmid_field = atomic64_read(&vmid->id) << VTTBR_VMID_SHIFT;
+ vmid_field &= VTTBR_VMID_MASK(kvm_get_vmid_bits());
return kvm_phys_to_vttbr(baddr) | vmid_field | cnp;
}

diff --git a/arch/arm64/kvm/hyp/tlb.c b/arch/arm64/kvm/hyp/tlb.c
index d49a14497715..46839c70461a 100644
--- a/arch/arm64/kvm/hyp/tlb.c
+++ b/arch/arm64/kvm/hyp/tlb.c
@@ -189,10 +189,10 @@ void __hyp_text __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu)
__tlb_switch_to_host()(kvm, &cxt);
}

-void __hyp_text __kvm_flush_vm_context(void)
+void __hyp_text __kvm_tlb_flush_local_all(void)
{
- dsb(ishst);
- __tlbi(alle1is);
- asm volatile("ic ialluis" : : );
- dsb(ish);
+ dsb(nshst);
+ __tlbi(alle1);
+ asm volatile("ic iallu" : : );
+ dsb(nsh);
}
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index f645c0fbf7ec..c01b6036c909 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -32,6 +32,7 @@
#include <asm/tlbflush.h>
#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
+#include <asm/lib_asid.h>
#include <asm/virt.h>
#include <asm/kvm_arm.h>
#include <asm/kvm_asm.h>
@@ -50,10 +51,10 @@ static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
/* Per-CPU variable containing the currently running vcpu. */
static DEFINE_PER_CPU(struct kvm_vcpu *, kvm_arm_running_vcpu);

-/* The VMID used in the VTTBR */
-static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
-static u32 kvm_next_vmid;
-static DEFINE_SPINLOCK(kvm_vmid_lock);
+static DEFINE_PER_CPU(atomic64_t, active_vmids);
+static DEFINE_PER_CPU(u64, reserved_vmids);
+
+struct asid_info vmid_info;

static bool vgic_present;

@@ -128,9 +129,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)

kvm_vgic_early_init(kvm);

- /* Mark the initial VMID generation invalid */
- kvm->arch.vmid.vmid_gen = 0;
-
/* The maximum number of VCPUs is limited by the host's GIC model */
kvm->arch.max_vcpus = vgic_present ?
kvm_vgic_get_max_vcpus() : KVM_MAX_VCPUS;
@@ -449,35 +447,9 @@ bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
return vcpu_mode_priv(vcpu);
}

-/* Just ensure a guest exit from a particular CPU */
-static void exit_vm_noop(void *info)
-{
-}
-
-void force_vm_exit(const cpumask_t *mask)
-{
- preempt_disable();
- smp_call_function_many(mask, exit_vm_noop, NULL, true);
- preempt_enable();
-}
-
-/**
- * need_new_vmid_gen - check that the VMID is still valid
- * @vmid: The VMID to check
- *
- * return true if there is a new generation of VMIDs being used
- *
- * The hardware supports a limited set of values with the value zero reserved
- * for the host, so we check if an assigned value belongs to a previous
- * generation, which which requires us to assign a new value. If we're the
- * first to use a VMID for the new generation, we must flush necessary caches
- * and TLBs on all CPUs.
- */
-static bool need_new_vmid_gen(struct kvm_vmid *vmid)
+static void vmid_flush_cpu_ctxt(void)
{
- u64 current_vmid_gen = atomic64_read(&kvm_vmid_gen);
- smp_rmb(); /* Orders read of kvm_vmid_gen and kvm->arch.vmid */
- return unlikely(READ_ONCE(vmid->vmid_gen) != current_vmid_gen);
+ kvm_call_hyp(__kvm_tlb_flush_local_all);
}

/**
@@ -487,48 +459,9 @@ static bool need_new_vmid_gen(struct kvm_vmid *vmid)
*/
static void update_vmid(struct kvm_vmid *vmid)
{
- if (!need_new_vmid_gen(vmid))
- return;
-
- spin_lock(&kvm_vmid_lock);
-
- /*
- * We need to re-check the vmid_gen here to ensure that if another vcpu
- * already allocated a valid vmid for this vm, then this vcpu should
- * use the same vmid.
- */
- if (!need_new_vmid_gen(vmid)) {
- spin_unlock(&kvm_vmid_lock);
- return;
- }
-
- /* First user of a new VMID generation? */
- if (unlikely(kvm_next_vmid == 0)) {
- atomic64_inc(&kvm_vmid_gen);
- kvm_next_vmid = 1;
-
- /*
- * On SMP we know no other CPUs can use this CPU's or each
- * other's VMID after force_vm_exit returns since the
- * kvm_vmid_lock blocks them from reentry to the guest.
- */
- force_vm_exit(cpu_all_mask);
- /*
- * Now broadcast TLB + ICACHE invalidation over the inner
- * shareable domain to make sure all data structures are
- * clean.
- */
- kvm_call_hyp(__kvm_flush_vm_context);
- }
+ int cpu = smp_processor_id();

- vmid->vmid = kvm_next_vmid;
- kvm_next_vmid++;
- kvm_next_vmid &= (1 << kvm_get_vmid_bits()) - 1;
-
- smp_wmb();
- WRITE_ONCE(vmid->vmid_gen, atomic64_read(&kvm_vmid_gen));
-
- spin_unlock(&kvm_vmid_lock);
+ asid_check_context(&vmid_info, &vmid->id, cpu);
}

static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
@@ -682,8 +615,6 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
*/
cond_resched();

- update_vmid(&vcpu->kvm->arch.vmid);
-
check_vcpu_requests(vcpu);

/*
@@ -693,6 +624,15 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
*/
preempt_disable();

+ /*
+ * The ASID/VMID allocator only tracks active VMIDs per
+ * physical CPU, and therefore the VMID allocated may not be
+ * preserved on VMID roll-over if the task was preempted,
+ * making a thread's VMID inactive. So we need to call
+ * update_vttbr in non-premptible context.
+ */
+ update_vmid(&vcpu->kvm->arch.vmid);
+
kvm_pmu_flush_hwstate(vcpu);

local_irq_disable();
@@ -731,8 +671,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
*/
smp_store_mb(vcpu->mode, IN_GUEST_MODE);

- if (ret <= 0 || need_new_vmid_gen(&vcpu->kvm->arch.vmid) ||
- kvm_request_pending(vcpu)) {
+ if (ret <= 0 || kvm_request_pending(vcpu)) {
vcpu->mode = OUTSIDE_GUEST_MODE;
isb(); /* Ensure work in x_flush_hwstate is committed */
kvm_pmu_sync_hwstate(vcpu);
@@ -1328,6 +1267,8 @@ static void cpu_hyp_reset(void)
{
if (!is_kernel_in_hyp_mode())
__hyp_reset_vectors();
+
+ kvm_call_hyp(__kvm_tlb_flush_local_all);
}

static void cpu_hyp_reinit(void)
@@ -1431,11 +1372,32 @@ static inline void hyp_cpu_pm_exit(void)

static int init_common_resources(void)
{
+ int err;
+
+ /*
+ * Initialize the ASID allocator telling it to allocate a single
+ * VMID per VM.
+ */
+ err = asid_allocator_init(&vmid_info, kvm_get_vmid_bits(), 1,
+ vmid_flush_cpu_ctxt);
+ if (err) {
+ kvm_err("Failed to initialize VMID allocator.\n");
+ return err;
+ }
+
+ vmid_info.active = &active_vmids;
+ vmid_info.reserved = &reserved_vmids;
+
kvm_set_ipa_limit();

return 0;
}

+static void free_common_resources(void)
+{
+ asid_allocator_free(&vmid_info);
+}
+
static int init_subsystems(void)
{
int err = 0;
@@ -1684,7 +1646,7 @@ int kvm_arch_init(void *opaque)

err = kvm_arm_init_sve();
if (err)
- return err;
+ goto out_err;

if (!in_hyp_mode) {
err = init_hyp_mode();
@@ -1707,6 +1669,7 @@ int kvm_arch_init(void *opaque)
if (!in_hyp_mode)
teardown_hyp_mode();
out_err:
+ free_common_resources();
return err;
}

--
2.11.0