[PATCH 3/5] KVM: PPC: Book3S HV: Improve handling of local vs. global TLB invalidations

Paul Mackerras
2012-11-22T18:49:08Z

When we change or remove a HPT (hashed page table) entry, we can do
either a global TLB invalidation (tlbie) that works across the whole
machine, or a local invalidation (tlbiel) that only affects this core.
Currently we do local invalidations if the VM has only one vcpu or if
the guest requests it with the H_LOCAL flag, though the guest Linux
kernel currently doesn't ever use H_LOCAL. Then, to cope with the
possibility that vcpus moving around to different physical cores might
expose stale TLB entries, there is some code in kvmppc_hv_entry to
flush the whole TLB of entries for this VM if either this vcpu is now
running on a different physical core from where it last ran, or if this
physical core last ran a different vcpu.

There are a number of problems on POWER7 with this as it stands:

- The TLB invalidation is done per thread, whereas it only needs to be
done per core, since the TLB is shared between the threads.
- With the possibility of the host paging out guest pages, the use of
H_LOCAL by an SMP guest is dangerous since the guest could possibly
retain and use a stale TLB entry pointing to a page that had been
removed from the guest.
- The TLB invalidations that we do when a vcpu moves from one physical
core to another are unnecessary in the case of an SMP guest that isn't
using H_LOCAL.
- The optimization of using local invalidations rather than global should
apply to guests with one virtual core, not just one vcpu.

(None of this applies on PPC970, since there we always have to
invalidate the whole TLB when entering and leaving the guest, and we
can't support paging out guest memory.)

To fix these problems and simplify the code, we now maintain a simple
cpumask of which cpus need to flush the TLB on entry to the guest.
(This is indexed by cpu, though we only ever use the bits for thread
0 of each core.) Whenever we do a local TLB invalidation, we set the
bits for every cpu except the bit for thread 0 of the core that we're
currently running on. Whenever we enter a guest, we test and clear the
bit for our core, and flush the TLB if it was set.

On initial startup of the VM, and when resetting the HPT, we set all the
bits in the need_tlb_flush cpumask, since any core could potentially have
stale TLB entries from the previous VM to use the same LPID, or the
previous contents of the HPT.

Then, we maintain a count of the number of online virtual cores, and use
that when deciding whether to use a local invalidation rather than the
number of online vcpus. The code to make that decision is extracted out
into a new function, global_invalidates(). For multi-core guests on
POWER7 (i.e. when we are using mmu notifiers), we now never do local
invalidations regardless of the H_LOCAL flag.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
arch/powerpc/include/asm/kvm_host.h | 5 +--
arch/powerpc/kernel/asm-offsets.c | 4 +--
arch/powerpc/kvm/book3s_64_mmu_hv.c | 7 ++--
arch/powerpc/kvm/book3s_hv.c | 9 ++++-
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 37 +++++++++++++++++---
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 56 ++++++++++++++-----------------
6 files changed, 73 insertions(+), 45 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 58c7264..62fbd38 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -246,11 +246,12 @@ struct kvm_arch {
int using_mmu_notifiers;
u32 hpt_order;
atomic_t vcpus_running;
+ u32 online_vcores;
unsigned long hpt_npte;
unsigned long hpt_mask;
atomic_t hpte_mod_interest;
spinlock_t slot_phys_lock;
- unsigned short last_vcpu[NR_CPUS];
+ cpumask_t need_tlb_flush;
struct kvmppc_vcore *vcores[KVM_MAX_VCORES];
struct kvmppc_linear_info *hpt_li;
#endif /* CONFIG_KVM_BOOK3S_64_HV */
@@ -275,6 +276,7 @@ struct kvmppc_vcore {
int nap_count;
int napping_threads;
u16 pcpu;
+ u16 last_cpu;
u8 vcore_state;
u8 in_guest;
struct list_head runnable_threads;
@@ -523,7 +525,6 @@ struct kvm_vcpu_arch {
u64 dec_jiffies;
u64 dec_expires;
unsigned long pending_exceptions;
- u16 last_cpu;
u8 ceded;
u8 prodded;
u32 last_inst;
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 7523539..4e23ba2 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -441,8 +441,7 @@ int main(void)
DEFINE(KVM_HOST_LPCR, offsetof(struct kvm, arch.host_lpcr));
DEFINE(KVM_HOST_SDR1, offsetof(struct kvm, arch.host_sdr1));
DEFINE(KVM_TLBIE_LOCK, offsetof(struct kvm, arch.tlbie_lock));
- DEFINE(KVM_ONLINE_CPUS, offsetof(struct kvm, online_vcpus.counter));
- DEFINE(KVM_LAST_VCPU, offsetof(struct kvm, arch.last_vcpu));
+ DEFINE(KVM_NEED_FLUSH, offsetof(struct kvm, arch.need_tlb_flush.bits));
DEFINE(KVM_LPCR, offsetof(struct kvm, arch.lpcr));
DEFINE(KVM_RMOR, offsetof(struct kvm, arch.rmor));
DEFINE(KVM_VRMA_SLB_V, offsetof(struct kvm, arch.vrma_slb_v));
@@ -470,7 +469,6 @@ int main(void)
DEFINE(VCPU_SLB, offsetof(struct kvm_vcpu, arch.slb));
DEFINE(VCPU_SLB_MAX, offsetof(struct kvm_vcpu, arch.slb_max));
DEFINE(VCPU_SLB_NR, offsetof(struct kvm_vcpu, arch.slb_nr));
- DEFINE(VCPU_LAST_CPU, offsetof(struct kvm_vcpu, arch.last_cpu));
DEFINE(VCPU_FAULT_DSISR, offsetof(struct kvm_vcpu, arch.fault_dsisr));
DEFINE(VCPU_FAULT_DAR, offsetof(struct kvm_vcpu, arch.fault_dar));
DEFINE(VCPU_LAST_INST, offsetof(struct kvm_vcpu, arch.last_inst));
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 1029e22..2d61e01 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -148,11 +148,8 @@ long kvmppc_alloc_reset_hpt(struct kvm *kvm, u32 *htab_orderp)
* Reset all the reverse-mapping chains for all memslots
*/
kvmppc_rmap_reset(kvm);
- /*
- * Set the whole last_vcpu array to an invalid vcpu number.
- * This ensures that each vcpu will flush its TLB on next entry.
- */
- memset(kvm->arch.last_vcpu, 0xff, sizeof(kvm->arch.last_vcpu));
+ /* Ensure that each vcpu will flush its TLB on next entry. */
+ cpumask_setall(&kvm->arch.need_tlb_flush);
*htab_orderp = order;
err = 0;
} else {
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index a4f59db..ddbec60 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -853,7 +853,6 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
goto free_vcpu;

vcpu->arch.shared = &vcpu->arch.shregs;
- vcpu->arch.last_cpu = -1;
vcpu->arch.mmcr[0] = MMCR0_FC;
vcpu->arch.ctrl = CTRL_RUNLATCH;
/* default to host PVR, since we can't spoof it */
@@ -880,6 +879,7 @@ struct kvm_vcpu *kvmppc_core_vcpu_create(struct kvm *kvm, unsigned int id)
vcore->preempt_tb = TB_NIL;
}
kvm->arch.vcores[core] = vcore;
+ kvm->arch.online_vcores++;
}
mutex_unlock(&kvm->lock);

@@ -1802,6 +1802,13 @@ int kvmppc_core_init_vm(struct kvm *kvm)
return -ENOMEM;
kvm->arch.lpid = lpid;

+ /*
+ * Since we don't flush the TLB when tearing down a VM,
+ * and this lpid might have previously been used,
+ * make sure we flush on each core before running the new VM.
+ */
+ cpumask_setall(&kvm->arch.need_tlb_flush);
+
INIT_LIST_HEAD(&kvm->arch.spapr_tce_tables);

kvm->arch.rma = NULL;
diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index fc3da32..7e1f7e2 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -35,6 +35,37 @@ static void *real_vmalloc_addr(void *x)
return __va(addr);
}

+/* Return 1 if we need to do a global tlbie, 0 if we can use tlbiel */
+static int global_invalidates(struct kvm *kvm, unsigned long flags)
+{
+ int global;
+
+ /*
+ * If there is only one vcore, and it's currently running,
+ * we can use tlbiel as long as we mark all other physical
+ * cores as potentially having stale TLB entries for this lpid.
+ * If we're not using MMU notifiers, we never take pages away
+ * from the guest, so we can use tlbiel if requested.
+ * Otherwise, don't use tlbiel.
+ */
+ if (kvm->arch.online_vcores == 1 && local_paca->kvm_hstate.kvm_vcore)
+ global = 0;
+ else if (kvm->arch.using_mmu_notifiers)
+ global = 1;
+ else
+ global = !(flags & H_LOCAL);
+
+ if (!global) {
+ /* any other core might now have stale TLB entries... */
+ smp_wmb();
+ cpumask_setall(&kvm->arch.need_tlb_flush);
+ cpumask_clear_cpu(local_paca->kvm_hstate.kvm_vcore->pcpu,
+ &kvm->arch.need_tlb_flush);
+ }
+
+ return global;
+}
+
/*
* Add this HPTE into the chain for the real page.
* Must be called with the chain locked; it unlocks the chain.
@@ -390,7 +421,7 @@ long kvmppc_do_h_remove(struct kvm *kvm, unsigned long flags,
if (v & HPTE_V_VALID) {
hpte[0] &= ~HPTE_V_VALID;
rb = compute_tlbie_rb(v, hpte[1], pte_index);
- if (!(flags & H_LOCAL) && atomic_read(&kvm->online_vcpus) > 1) {
+ if (global_invalidates(kvm, flags)) {
while (!try_lock_tlbie(&kvm->arch.tlbie_lock))
cpu_relax();
asm volatile("ptesync" : : : "memory");
@@ -565,8 +596,6 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsigned long flags,
return H_NOT_FOUND;
}

- if (atomic_read(&kvm->online_vcpus) == 1)
- flags |= H_LOCAL;
v = hpte[0];
bits = (flags << 55) & HPTE_R_PP0;
bits |= (flags << 48) & HPTE_R_KEY_HI;
@@ -587,7 +616,7 @@ long kvmppc_h_protect(struct kvm_vcpu *vcpu, unsigned long flags,
if (v & HPTE_V_VALID) {
rb = compute_tlbie_rb(v, r, pte_index);
hpte[0] = v & ~HPTE_V_VALID;
- if (!(flags & H_LOCAL)) {
+ if (global_invalidates(kvm, flags)) {
while(!try_lock_tlbie(&kvm->arch.tlbie_lock))
cpu_relax();
asm volatile("ptesync" : : : "memory");
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index b31fb4f..dbb5ced 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -313,7 +313,33 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
mtspr SPRN_SDR1,r6 /* switch to partition page table */
mtspr SPRN_LPID,r7
isync
+
+ /* See if we need to flush the TLB */
+ lhz r6,PACAPACAINDEX(r13) /* test_bit(cpu, need_tlb_flush) */
+ clrldi r7,r6,64-6 /* extract bit number (6 bits) */
+ srdi r6,r6,6 /* doubleword number */
+ sldi r6,r6,3 /* address offset */
+ add r6,r6,r9
+ addi r6,r6,KVM_NEED_FLUSH /* dword in kvm->arch.need_tlb_flush */
li r0,1
+ sld r0,r0,r7
+ ld r7,0(r6)
+ and. r7,r7,r0
+ beq 22f
+23: ldarx r7,0,r6 /* if set, clear the bit */
+ andc r7,r7,r0
+ stdcx. r7,0,r6
+ bne 23b
+ li r6,128 /* and flush the TLB */
+ mtctr r6
+ li r7,0x800 /* IS field = 0b10 */
+ ptesync
+28: tlbiel r7
+ addi r7,r7,0x1000
+ bdnz 28b
+ ptesync
+
+22: li r0,1
stb r0,VCORE_IN_GUEST(r5) /* signal secondaries to continue */
b 10f

@@ -336,36 +362,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_201)
mr r9,r4
blt hdec_soon

- /*
- * Invalidate the TLB if we could possibly have stale TLB
- * entries for this partition on this core due to the use
- * of tlbiel.
- * XXX maybe only need this on primary thread?
- */
- ld r9,VCPU_KVM(r4) /* pointer to struct kvm */
- lwz r5,VCPU_VCPUID(r4)
- lhz r6,PACAPACAINDEX(r13)
- rldimi r6,r5,0,62 /* XXX map as if threads 1:1 p:v */
- lhz r8,VCPU_LAST_CPU(r4)
- sldi r7,r6,1 /* see if this is the same vcpu */
- add r7,r7,r9 /* as last ran on this pcpu */
- lhz r0,KVM_LAST_VCPU(r7)
- cmpw r6,r8 /* on the same cpu core as last time? */
- bne 3f
- cmpw r0,r5 /* same vcpu as this core last ran? */
- beq 1f
-3: sth r6,VCPU_LAST_CPU(r4) /* if not, invalidate partition TLB */
- sth r5,KVM_LAST_VCPU(r7)
- li r6,128
- mtctr r6
- li r7,0x800 /* IS field = 0b10 */
- ptesync
-2: tlbiel r7
- addi r7,r7,0x1000
- bdnz 2b
- ptesync
-1:
-
/* Save purr/spurr */
mfspr r5,SPRN_PURR
mfspr r6,SPRN_SPURR
--
1.7.10.rc3.219.g53414