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Subject[PATCH v4 09/11] powerpc/kvm/book3s_64: Applies counting method to monitor lockless pgtbl walks
Date
Applies the counting-based method for monitoring all book3s_64-related
functions that do lockless pagetable walks.

Adds comments explaining that some lockless pagetable walks don't need
protection due to guest pgd not being a target of THP collapse/split, or
due to being called from Realmode + MSR_EE = 0.

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
arch/powerpc/kvm/book3s_64_mmu_hv.c | 2 ++
arch/powerpc/kvm/book3s_64_mmu_radix.c | 30 ++++++++++++++++++++++++++
arch/powerpc/kvm/book3s_64_vio_hv.c | 3 +++
3 files changed, 35 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 9a75f0e1933b..fcd3dad1297f 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -620,6 +620,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
* We need to protect against page table destruction
* hugepage split and collapse.
*/
+ start_lockless_pgtbl_walk(kvm->mm);
local_irq_save(flags);
ptep = find_current_mm_pte(current->mm->pgd,
hva, NULL, NULL);
@@ -629,6 +630,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
write_ok = 1;
}
local_irq_restore(flags);
+ end_lockless_pgtbl_walk(kvm->mm);
}
}

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 2d415c36a61d..9b374b9838fa 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -813,6 +813,7 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
* Read the PTE from the process' radix tree and use that
* so we get the shift and attribute bits.
*/
+ start_lockless_pgtbl_walk(kvm->mm);
local_irq_disable();
ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
/*
@@ -821,12 +822,14 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
*/
if (!ptep) {
local_irq_enable();
+ end_lockless_pgtbl_walk(kvm->mm);
if (page)
put_page(page);
return RESUME_GUEST;
}
pte = *ptep;
local_irq_enable();
+ end_lockless_pgtbl_walk(kvm->mm);

/* If we're logging dirty pages, always map single pages */
large_enable = !(memslot->flags & KVM_MEM_LOG_DIRTY_PAGES);
@@ -972,10 +975,16 @@ int kvm_unmap_radix(struct kvm *kvm, struct kvm_memory_slot *memslot,
unsigned long gpa = gfn << PAGE_SHIFT;
unsigned int shift;

+ /*
+ * We are walking the secondary (partition-scoped) page table here.
+ * We can do this without disabling irq because the Linux MM
+ * subsystem doesn't do THP splits and collapses on this tree.
+ */
ptep = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
if (ptep && pte_present(*ptep))
kvmppc_unmap_pte(kvm, ptep, gpa, shift, memslot,
kvm->arch.lpid);
+
return 0;
}

@@ -989,6 +998,11 @@ int kvm_age_radix(struct kvm *kvm, struct kvm_memory_slot *memslot,
int ref = 0;
unsigned long old, *rmapp;

+ /*
+ * We are walking the secondary (partition-scoped) page table here.
+ * We can do this without disabling irq because the Linux MM
+ * subsystem doesn't do THP splits and collapses on this tree.
+ */
ptep = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
if (ptep && pte_present(*ptep) && pte_young(*ptep)) {
old = kvmppc_radix_update_pte(kvm, ptep, _PAGE_ACCESSED, 0,
@@ -1013,6 +1027,11 @@ int kvm_test_age_radix(struct kvm *kvm, struct kvm_memory_slot *memslot,
unsigned int shift;
int ref = 0;

+ /*
+ * We are walking the secondary (partition-scoped) page table here.
+ * We can do this without disabling irq because the Linux MM
+ * subsystem doesn't do THP splits and collapses on this tree.
+ */
ptep = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
if (ptep && pte_present(*ptep) && pte_young(*ptep))
ref = 1;
@@ -1030,6 +1049,11 @@ static int kvm_radix_test_clear_dirty(struct kvm *kvm,
int ret = 0;
unsigned long old, *rmapp;

+ /*
+ * We are walking the secondary (partition-scoped) page table here.
+ * We can do this without disabling irq because the Linux MM
+ * subsystem doesn't do THP splits and collapses on this tree.
+ */
ptep = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
if (ptep && pte_present(*ptep) && pte_dirty(*ptep)) {
ret = 1;
@@ -1046,6 +1070,7 @@ static int kvm_radix_test_clear_dirty(struct kvm *kvm,
1UL << shift);
spin_unlock(&kvm->mmu_lock);
}
+
return ret;
}

@@ -1085,6 +1110,11 @@ void kvmppc_radix_flush_memslot(struct kvm *kvm,
gpa = memslot->base_gfn << PAGE_SHIFT;
spin_lock(&kvm->mmu_lock);
for (n = memslot->npages; n; --n) {
+ /*
+ * We are walking the secondary (partition-scoped) page table here.
+ * We can do this without disabling irq because the Linux MM
+ * subsystem doesn't do THP splits and collapses on this tree.
+ */
ptep = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
if (ptep && pte_present(*ptep))
kvmppc_unmap_pte(kvm, ptep, gpa, shift, memslot,
diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
index b4f20f13b860..376d069a92dd 100644
--- a/arch/powerpc/kvm/book3s_64_vio_hv.c
+++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
@@ -431,6 +431,7 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
static long kvmppc_rm_ua_to_hpa(struct kvm_vcpu *vcpu,
unsigned long ua, unsigned long *phpa)
{
+ struct kvm *kvm = vcpu->kvm;
pte_t *ptep, pte;
unsigned shift = 0;

@@ -443,10 +444,12 @@ static long kvmppc_rm_ua_to_hpa(struct kvm_vcpu *vcpu,
* to exit which will agains result in the below page table walk
* to finish.
*/
+ start_lockless_pgtbl_walk(kvm->mm);
ptep = __find_linux_pte(vcpu->arch.pgdir, ua, NULL, &shift);
if (!ptep || !pte_present(*ptep))
return -ENXIO;
pte = *ptep;
+ end_lockless_pgtbl_walk(kvm->mm);

if (!shift)
shift = PAGE_SHIFT;
--
2.20.1
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