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Date: Tue, 12 Oct 2021 18:14:30 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>
Cc: Suleiman Souhlal <suleiman@...gle.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH] KVM: MMU: make PTE_PREFETCH_NUM tunable
Turn PTE_PREFETCH_NUM into a module parameter, so that it
can be tuned per-VM.
- /sys/module/kvm/parameters/pte_prefetch_num 8
VM-EXIT Samples Samples% Time% Min Time Max Time Avg time
EPT_VIOLATION 760998 54.85% 7.23% 0.92us 31765.89us 7.78us ( +- 1.46% )
MSR_WRITE 170599 12.30% 0.53% 0.60us 3334.13us 2.52us ( +- 0.86% )
EXTERNAL_INTERRUPT 159510 11.50% 1.65% 0.49us 43705.81us 8.45us ( +- 7.54% )
[..]
Total Samples:1387305, Total events handled time:81900258.99us.
- /sys/module/kvm/parameters/pte_prefetch_num 16
VM-EXIT Samples Samples% Time% Min Time Max Time Avg time
EPT_VIOLATION 658064 52.58% 7.04% 0.91us 17022.84us 8.34us ( +- 1.52% )
MSR_WRITE 163776 13.09% 0.54% 0.56us 5192.10us 2.57us ( +- 1.25% )
EXTERNAL_INTERRUPT 144588 11.55% 1.62% 0.48us 97410.16us 8.75us ( +- 11.44% )
[..]
Total Samples:1251546, Total events handled time:77956187.56us.
Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
arch/x86/kvm/mmu/mmu.c | 31 ++++++++++++++++++++++---------
1 file changed, 22 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 24a9f4c3f5e7..0ab4490674ec 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -115,6 +115,8 @@ module_param(dbg, bool, 0644);
#endif
#define PTE_PREFETCH_NUM 8
+static uint __read_mostly pte_prefetch_num = PTE_PREFETCH_NUM;
+module_param(pte_prefetch_num, uint, 0644);
#define PT32_LEVEL_BITS 10
@@ -732,7 +734,7 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
/* 1 rmap, 1 parent PTE per level, and the prefetched rmaps. */
r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache,
- 1 + PT64_ROOT_MAX_LEVEL + PTE_PREFETCH_NUM);
+ 1 + PT64_ROOT_MAX_LEVEL + pte_prefetch_num);
if (r)
return r;
r = kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_shadow_page_cache,
@@ -2753,20 +2755,29 @@ static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp,
u64 *start, u64 *end)
{
- struct page *pages[PTE_PREFETCH_NUM];
+ struct page **pages;
struct kvm_memory_slot *slot;
unsigned int access = sp->role.access;
int i, ret;
gfn_t gfn;
+ pages = kmalloc_array(pte_prefetch_num, sizeof(struct page *),
+ GFP_KERNEL);
+ if (!pages)
+ return -1;
+
gfn = kvm_mmu_page_get_gfn(sp, start - sp->spt);
slot = gfn_to_memslot_dirty_bitmap(vcpu, gfn, access & ACC_WRITE_MASK);
- if (!slot)
- return -1;
+ if (!slot) {
+ ret = -1;
+ goto out;
+ }
ret = gfn_to_page_many_atomic(slot, gfn, pages, end - start);
- if (ret <= 0)
- return -1;
+ if (ret <= 0) {
+ ret = -1;
+ goto out;
+ }
for (i = 0; i < ret; i++, gfn++, start++) {
mmu_set_spte(vcpu, slot, start, access, gfn,
@@ -2774,7 +2785,9 @@ static int direct_pte_prefetch_many(struct kvm_vcpu *vcpu,
put_page(pages[i]);
}
- return 0;
+out:
+ kfree(pages);
+ return ret;
}
static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
@@ -2785,10 +2798,10 @@ static void __direct_pte_prefetch(struct kvm_vcpu *vcpu,
WARN_ON(!sp->role.direct);
- i = (sptep - sp->spt) & ~(PTE_PREFETCH_NUM - 1);
+ i = (sptep - sp->spt) & ~(pte_prefetch_num - 1);
spte = sp->spt + i;
- for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
+ for (i = 0; i < pte_prefetch_num; i++, spte++) {
if (is_shadow_present_pte(*spte) || spte == sptep) {
if (!start)
continue;
--
2.33.0.882.g93a45727a2-goog
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