From: Yanan Wang <wangyanan55@huawei.com>
To: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
"Catalin Marinas" <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
"Julien Thierry" <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
<kvmarm@lists.cs.columbia.edu>,
<linux-arm-kernel@lists.infradead.org>, <kvm@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Cc: <wanghaibin.wang@huawei.com>, <yuzenghui@huawei.com>,
Yanan Wang <wangyanan55@huawei.com>
Subject: [PATCH 1/2] KVM: arm64: Distinguish cases of allocating memcache more precisely
Date: Mon, 25 Jan 2021 22:10:43 +0800 [thread overview]
Message-ID: <20210125141044.380156-2-wangyanan55@huawei.com> (raw)
In-Reply-To: <20210125141044.380156-1-wangyanan55@huawei.com>
With a guest translation fault, we don't really need the memcache pages
when only installing a new entry to the existing page table or replacing
the table entry with a block entry. And with a guest permission fault,
we also don't need the memcache pages for a write_fault in dirty-logging
time if VMs are not configured with huge mappings.
The cases where allocations from memcache are required can be much more
precisely distinguished by comparing fault_granule and vma_pagesize.
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
---
arch/arm64/kvm/mmu.c | 25 ++++++++++++-------------
1 file changed, 12 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 7d2257cc5438..8e8549ea1d70 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -820,19 +820,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
gfn = fault_ipa >> PAGE_SHIFT;
mmap_read_unlock(current->mm);
- /*
- * Permission faults just need to update the existing leaf entry,
- * and so normally don't require allocations from the memcache. The
- * only exception to this is when dirty logging is enabled at runtime
- * and a write fault needs to collapse a block entry into a table.
- */
- if (fault_status != FSC_PERM || (logging_active && write_fault)) {
- ret = kvm_mmu_topup_memory_cache(memcache,
- kvm_mmu_cache_min_pages(kvm));
- if (ret)
- return ret;
- }
-
mmu_seq = vcpu->kvm->mmu_notifier_seq;
/*
* Ensure the read of mmu_notifier_seq happens before we call
@@ -898,6 +885,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC))
prot |= KVM_PGTABLE_PROT_X;
+ /*
+ * Allocations from the memcache are required only when granule of the
+ * lookup level where a guest fault happened exceeds the vma_pagesize,
+ * which means new page tables will be created in the fault handlers.
+ */
+ if (fault_granule > vma_pagesize) {
+ ret = kvm_mmu_topup_memory_cache(memcache,
+ kvm_mmu_cache_min_pages(kvm));
+ if (ret)
+ return ret;
+ }
+
/*
* Under the premise of getting a FSC_PERM fault, we just need to relax
* permissions only if vma_pagesize equals fault_granule. Otherwise,
--
2.19.1
next prev parent reply other threads:[~2021-01-25 14:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 14:10 [PATCH 0/2] Performance improvement about cache flush Yanan Wang
2021-01-25 14:10 ` Yanan Wang [this message]
2021-03-08 16:35 ` [PATCH 1/2] KVM: arm64: Distinguish cases of allocating memcache more precisely Will Deacon
2021-01-25 14:10 ` [PATCH 2/2] KVM: arm64: Skip the cache flush when coalescing tables into a block Yanan Wang
2021-03-08 16:34 ` Will Deacon
2021-03-09 8:34 ` wangyanan (Y)
2021-03-09 8:43 ` Marc Zyngier
2021-03-09 9:02 ` wangyanan (Y)
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