[PATCH v4 08/11] powerpc/kvm/book3s_hv: Applies counting method to monitor lockless pgtbl walks

Leonardo Bras
2019-09-27T23:40:05Z

Applies the counting-based method for monitoring all book3s_hv 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

kvmppc_do_h_enter: Fixes where local_irq_restore() must be placed (after
the last usage of ptep).

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
arch/powerpc/kvm/book3s_hv_nested.c | 22 ++++++++++++++++++++--
arch/powerpc/kvm/book3s_hv_rm_mmu.c | 18 ++++++++++++++----
2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index 735e0ac6f5b2..5a641b559de7 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -803,7 +803,11 @@ static void kvmhv_update_nest_rmap_rc(struct kvm *kvm, u64 n_rmap,
if (!gp)
return;

- /* Find the pte */
+ /* Find the pte:
+ * We are walking the nested guest (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(gp->shadow_pgtable, gpa, NULL, &shift);
/*
* If the pte is present and the pfn is still the same, update the pte.
@@ -853,7 +857,11 @@ static void kvmhv_remove_nest_rmap(struct kvm *kvm, u64 n_rmap,
if (!gp)
return;

- /* Find and invalidate the pte */
+ /* Find and invalidate the pte:
+ * We are walking the nested guest (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(gp->shadow_pgtable, gpa, NULL, &shift);
/* Don't spuriously invalidate ptes if the pfn has changed */
if (ptep && pte_present(*ptep) && ((pte_val(*ptep) & mask) == hpa))
@@ -921,6 +929,11 @@ static bool kvmhv_invalidate_shadow_pte(struct kvm_vcpu *vcpu,
int shift;

spin_lock(&kvm->mmu_lock);
+ /*
+ * We are walking the nested guest (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(gp->shadow_pgtable, gpa, NULL, &shift);
if (!shift)
shift = PAGE_SHIFT;
@@ -1362,6 +1375,11 @@ static long int __kvmhv_nested_page_fault(struct kvm_run *run,
/* See if can find translation in our partition scoped tables for L1 */
pte = __pte(0);
spin_lock(&kvm->mmu_lock);
+ /*
+ * 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.
+ */
pte_p = __find_linux_pte(kvm->arch.pgtable, gpa, NULL, &shift);
if (!shift)
shift = PAGE_SHIFT;
diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
index 63e0ce91e29d..2076a7ac230a 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
@@ -252,6 +252,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
* If we had a page table table change after lookup, we would
* retry via mmu_notifier_retry.
*/
+ start_lockless_pgtbl_walk(kvm->mm);
if (!realmode)
local_irq_save(irq_flags);
/*
@@ -287,8 +288,6 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
pa |= gpa & ~PAGE_MASK;
}
}
- if (!realmode)
- local_irq_restore(irq_flags);

ptel &= HPTE_R_KEY | HPTE_R_PP0 | (psize-1);
ptel |= pa;
@@ -311,6 +310,9 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
ptel &= ~(HPTE_R_W|HPTE_R_I|HPTE_R_G);
ptel |= HPTE_R_M;
}
+ if (!realmode)
+ local_irq_restore(irq_flags);
+ end_lockless_pgtbl_walk(kvm->mm);

/* Find and lock the HPTEG slot to use */
do_insert:
@@ -885,11 +887,19 @@ static int kvmppc_get_hpa(struct kvm_vcpu *vcpu, unsigned long gpa,
/* Translate to host virtual address */
hva = __gfn_to_hva_memslot(memslot, gfn);

- /* Try to find the host pte for that virtual address */
+ /* Try to find the host pte for that virtual address :
+ * Called by hcall_real_table (real mode + MSR_EE=0)
+ * Interrupts are disabled here.
+ */
+ start_lockless_pgtbl_walk(kvm->mm);
ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
- if (!ptep)
+ if (!ptep) {
+ end_lockless_pgtbl_walk(kvm->mm);
return H_TOO_HARD;
+ }
pte = kvmppc_read_update_linux_pte(ptep, writing);
+ end_lockless_pgtbl_walk(kvm->mm);
+
if (!pte_present(pte))
return H_TOO_HARD;

--
2.20.1