Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-mm@kvack.org
Cc:     Leonardo Bras <leonardo@linux.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>,
        Allison Randal <allison@lohutok.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ganesh Goudar <ganeshgr@linux.ibm.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ira Weiny <ira.weiny@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        John Hubbard <jhubbard@nvidia.com>,
        Keith Busch <keith.busch@intel.com>
Subject: [PATCH v4 08/11] powerpc/kvm/book3s_hv: Applies counting method to monitor lockless pgtbl walks
Date:   Fri, 27 Sep 2019 20:40:05 -0300
Message-Id: <20190927234008.11513-9-leonardo@linux.ibm.com>
In-Reply-To: <20190927234008.11513-1-leonardo@linux.ibm.com>
References: <20190927234008.11513-1-leonardo@linux.ibm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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