[PATCH v5 09/11] powerpc/kvm/book3s_64: Applies counting method to monitor lockless pgtbl walks
Leonardo Bras
leonardo at linux.ibm.com
Thu Oct 3 11:33:23 AEST 2019
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.
Given that some of these functions always are called in realmode, we use
__{begin,end}_lockless_pgtbl_walk so we can decide when to disable
interrupts.
local_irq_{save,restore} is already inside {begin,end}_lockless_pgtbl_walk,
so there is no need to repeat it here.
Variable that saves the irq mask was renamed from flags to irq_mask so it
doesn't lose meaning now it's not directly passed to local_irq_* functions.
There are also a function that uses local_irq_{en,dis}able, so the return
value of begin_lockless_pgtbl_walk() is ignored and we pass IRQS_ENABLED to
end_lockless_pgtbl_walk() to mimic the effect of local_irq_enable().
Signed-off-by: Leonardo Bras <leonardo at linux.ibm.com>
---
arch/powerpc/kvm/book3s_64_mmu_hv.c | 6 ++---
arch/powerpc/kvm/book3s_64_mmu_radix.c | 34 +++++++++++++++++++++++---
arch/powerpc/kvm/book3s_64_vio_hv.c | 7 +++++-
3 files changed, 40 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 9a75f0e1933b..d8f374c979f5 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -615,12 +615,12 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
/* if the guest wants write access, see if that is OK */
if (!writing && hpte_is_writable(r)) {
pte_t *ptep, pte;
- unsigned long flags;
+ unsigned long irq_mask;
/*
* We need to protect against page table destruction
* hugepage split and collapse.
*/
- local_irq_save(flags);
+ irq_mask = begin_lockless_pgtbl_walk(kvm->mm);
ptep = find_current_mm_pte(current->mm->pgd,
hva, NULL, NULL);
if (ptep) {
@@ -628,7 +628,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
if (__pte_write(pte))
write_ok = 1;
}
- local_irq_restore(flags);
+ end_lockless_pgtbl_walk(kvm->mm, irq_mask);
}
}
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 2d415c36a61d..8ba9742e2fc8 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -813,20 +813,20 @@ 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.
*/
- local_irq_disable();
+ begin_lockless_pgtbl_walk(kvm->mm);
ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
/*
* If the PTE disappeared temporarily due to a THP
* collapse, just return and let the guest try again.
*/
if (!ptep) {
- local_irq_enable();
+ end_lockless_pgtbl_walk(kvm->mm, IRQS_ENABLED);
if (page)
put_page(page);
return RESUME_GUEST;
}
pte = *ptep;
- local_irq_enable();
+ end_lockless_pgtbl_walk(kvm->mm, IRQS_ENABLED);
/* If we're logging dirty pages, always map single pages */
large_enable = !(memslot->flags & KVM_MEM_LOG_DIRTY_PAGES);
@@ -972,10 +972,16 @@ 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 +995,11 @@ 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 +1024,11 @@ 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 +1046,11 @@ 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 +1067,7 @@ static int kvm_radix_test_clear_dirty(struct kvm *kvm,
1UL << shift);
spin_unlock(&kvm->mmu_lock);
}
+
return ret;
}
@@ -1085,6 +1107,12 @@ 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 ab6eeb8e753e..0091c3d0ce89 100644
--- a/arch/powerpc/kvm/book3s_64_vio_hv.c
+++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
@@ -441,6 +441,7 @@ 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;
@@ -453,10 +454,14 @@ 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.
*/
+ __begin_lockless_pgtbl_walk(kvm->mm, false);
ptep = __find_linux_pte(vcpu->arch.pgdir, ua, NULL, &shift);
- if (!ptep || !pte_present(*ptep))
+ if (!ptep || !pte_present(*ptep)) {
+ __end_lockless_pgtbl_walk(kvm->mm, 0, false);
return -ENXIO;
+ }
pte = *ptep;
+ __end_lockless_pgtbl_walk(kvm->mm, 0, false);
if (!shift)
shift = PAGE_SHIFT;
--
2.20.1
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