From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Marc Zyngier <maz@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Arnd Bergmann <arnd@arndb.de>
Cc: linux-arch@vger.kernel.org, Junaid Shahid <junaids@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
kvm@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
Peter Shier <pshier@google.com>,
linux-mips@vger.kernel.org,
Sean Christopherson <sean.j.christopherson@intel.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Ben Gardon <bgardon@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Peter Feiner <pfeiner@google.com>,
kvmarm@lists.cs.columbia.edu, Jim Mattson <jmattson@google.com>
Subject: [PATCH v2 08/21] KVM: x86/mmu: Clean up the gorilla math in mmu_topup_memory_caches()
Date: Mon, 22 Jun 2020 13:08:09 -0700 [thread overview]
Message-ID: <20200622200822.4426-9-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20200622200822.4426-1-sean.j.christopherson@intel.com>
Clean up the minimums in mmu_topup_memory_caches() to document the
driving mechanisms behind the minimums. Now that encountering an empty
cache is unlikely to trigger BUG_ON(), it is less dangerous to be more
precise when defining the minimums.
For rmaps, the logic is 1 parent PTE per level, plus a single rmap, and
prefetched rmaps. The extra objects in the current '8 + PREFETCH'
minimum came about due to an abundance of paranoia in commit
c41ef344de212 ("KVM: MMU: increase per-vcpu rmap cache alloc size"),
i.e. it could have increased the minimum to 2 rmaps. Furthermore, the
unexpected extra rmap case was killed off entirely by commits
f759e2b4c728c ("KVM: MMU: avoid pte_list_desc running out in
kvm_mmu_pte_write") and f5a1e9f89504f ("KVM: MMU: remove call to
kvm_mmu_pte_write from walk_addr").
For the so called page cache, replace '8' with 2*PT64_ROOT_MAX_LEVEL.
The 2x multiplier is needed because the cache is used for both shadow
pages and gfn arrays for indirect MMUs.
And finally, for page headers, replace '4' with PT64_ROOT_MAX_LEVEL.
Note, KVM now supports 5-level paging, i.e. the old minimums that used a
baseline derived from 4-level paging were technically wrong. But, KVM
always allocates roots in a separate flow, e.g. it's impossible in the
current implementation to actually need 5 new shadow pages in a single
flow. Use PT64_ROOT_MAX_LEVEL unmodified instead of subtracting 1, as
the direct usage is likely more intuitive to uninformed readers, and the
inflated minimum is unlikely to affect functionality in practice.
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/mmu/mmu.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4b4c3234d623..451e0365e5dd 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1103,14 +1103,17 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu)
{
int r;
+ /* 1 rmap, 1 parent PTE per level, and the prefetched rmaps. */
r = mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache,
- 8 + PTE_PREFETCH_NUM);
+ 1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
if (r)
return r;
- r = mmu_topup_memory_cache(&vcpu->arch.mmu_page_cache, 8);
+ r = mmu_topup_memory_cache(&vcpu->arch.mmu_page_cache,
+ 2 * PT64_ROOT_MAX_LEVEL);
if (r)
return r;
- return mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache, 4);
+ return mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache,
+ PT64_ROOT_MAX_LEVEL);
}
static void mmu_free_memory_caches(struct kvm_vcpu *vcpu)
--
2.26.0
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next prev parent reply other threads:[~2020-06-22 20:09 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-22 20:08 [PATCH v2 00/21] KVM: Cleanup and unify kvm_mmu_memory_cache usage Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 01/21] KVM: x86/mmu: Track the associated kmem_cache in the MMU caches Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 02/21] KVM: x86/mmu: Consolidate "page" variant of memory cache helpers Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 03/21] KVM: x86/mmu: Use consistent "mc" name for kvm_mmu_memory_cache locals Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 04/21] KVM: x86/mmu: Remove superfluous gotos from mmu_topup_memory_caches() Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 05/21] KVM: x86/mmu: Try to avoid crashing KVM if a MMU memory cache is empty Sean Christopherson
2020-06-24 18:03 ` Ben Gardon
2020-06-22 20:08 ` [PATCH v2 06/21] KVM: x86/mmu: Move fast_page_fault() call above mmu_topup_memory_caches() Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 07/21] KVM: x86/mmu: Topup memory caches after walking GVA->GPA Sean Christopherson
2020-06-22 20:08 ` Sean Christopherson [this message]
2020-06-22 20:08 ` [PATCH v2 09/21] KVM: x86/mmu: Separate the memory caches for shadow pages and gfn arrays Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 10/21] KVM: x86/mmu: Make __GFP_ZERO a property of the memory cache Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 11/21] KVM: x86/mmu: Zero allocate shadow pages (outside of mmu_lock) Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 12/21] KVM: x86/mmu: Skip filling the gfn cache for guaranteed direct MMU topups Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 13/21] KVM: x86/mmu: Prepend "kvm_" to memory cache helpers that will be global Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 14/21] KVM: Move x86's version of struct kvm_mmu_memory_cache to common code Sean Christopherson
2020-06-24 18:08 ` Ben Gardon
2020-06-22 20:08 ` [PATCH v2 15/21] KVM: Move x86's MMU memory cache helpers to common KVM code Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 16/21] KVM: arm64: Drop @max param from mmu_topup_memory_cache() Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 17/21] KVM: arm64: Use common code's approach for __GFP_ZERO with memory caches Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 18/21] KVM: arm64: Use common KVM implementation of MMU " Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 19/21] KVM: MIPS: Drop @max param from mmu_topup_memory_cache() Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 20/21] KVM: MIPS: Account pages used for GPA page tables Sean Christopherson
2020-06-22 20:08 ` [PATCH v2 21/21] KVM: MIPS: Use common KVM implementation of MMU memory caches Sean Christopherson
2020-06-23 17:26 ` [PATCH v2 00/21] KVM: Cleanup and unify kvm_mmu_memory_cache usage Sean Christopherson
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