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KVM: switch to get_user_pages_fast
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Convert gfn_to_pfn to use get_user_pages_fast, which can do lockless
pagetable lookups on x86. Kernel compilation on 4-way guest is 3.7%
faster on VMX.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
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Marcelo Tosatti authored and Avi Kivity committed Oct 15, 2008
1 parent 777b3f4 commit 4c2155c
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Showing 6 changed files with 15 additions and 38 deletions.
2 changes: 0 additions & 2 deletions arch/powerpc/kvm/44x_tlb.c
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Original file line number Diff line number Diff line change
Expand Up @@ -147,9 +147,7 @@ void kvmppc_mmu_map(struct kvm_vcpu *vcpu, u64 gvaddr, gfn_t gfn, u64 asid,
stlbe = &vcpu->arch.shadow_tlb[victim];

/* Get reference to new page. */
down_read(&current->mm->mmap_sem);
new_page = gfn_to_page(vcpu->kvm, gfn);
up_read(&current->mm->mmap_sem);
if (is_error_page(new_page)) {
printk(KERN_ERR "Couldn't get guest page for gfn %lx!\n", gfn);
kvm_release_page_clean(new_page);
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23 changes: 9 additions & 14 deletions arch/x86/kvm/mmu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -405,16 +405,19 @@ static int host_largepage_backed(struct kvm *kvm, gfn_t gfn)
{
struct vm_area_struct *vma;
unsigned long addr;
int ret = 0;

addr = gfn_to_hva(kvm, gfn);
if (kvm_is_error_hva(addr))
return 0;
return ret;

down_read(&current->mm->mmap_sem);
vma = find_vma(current->mm, addr);
if (vma && is_vm_hugetlb_page(vma))
return 1;
ret = 1;
up_read(&current->mm->mmap_sem);

return 0;
return ret;
}

static int is_largepage_backed(struct kvm_vcpu *vcpu, gfn_t large_gfn)
Expand Down Expand Up @@ -1140,9 +1143,7 @@ struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva)
if (gpa == UNMAPPED_GVA)
return NULL;

down_read(&current->mm->mmap_sem);
page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
up_read(&current->mm->mmap_sem);

return page;
}
Expand Down Expand Up @@ -1330,16 +1331,14 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
pfn_t pfn;
unsigned long mmu_seq;

down_read(&current->mm->mmap_sem);
if (is_largepage_backed(vcpu, gfn & ~(KVM_PAGES_PER_HPAGE-1))) {
gfn &= ~(KVM_PAGES_PER_HPAGE-1);
largepage = 1;
}

mmu_seq = vcpu->kvm->mmu_notifier_seq;
/* implicit mb(), we'll read before PT lock is unlocked */
smp_rmb();
pfn = gfn_to_pfn(vcpu->kvm, gfn);
up_read(&current->mm->mmap_sem);

/* mmio */
if (is_error_pfn(pfn)) {
Expand Down Expand Up @@ -1488,15 +1487,13 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
if (r)
return r;

down_read(&current->mm->mmap_sem);
if (is_largepage_backed(vcpu, gfn & ~(KVM_PAGES_PER_HPAGE-1))) {
gfn &= ~(KVM_PAGES_PER_HPAGE-1);
largepage = 1;
}
mmu_seq = vcpu->kvm->mmu_notifier_seq;
/* implicit mb(), we'll read before PT lock is unlocked */
smp_rmb();
pfn = gfn_to_pfn(vcpu->kvm, gfn);
up_read(&current->mm->mmap_sem);
if (is_error_pfn(pfn)) {
kvm_release_pfn_clean(pfn);
return 1;
Expand Down Expand Up @@ -1809,15 +1806,13 @@ static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
return;
gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;

down_read(&current->mm->mmap_sem);
if (is_large_pte(gpte) && is_largepage_backed(vcpu, gfn)) {
gfn &= ~(KVM_PAGES_PER_HPAGE-1);
vcpu->arch.update_pte.largepage = 1;
}
vcpu->arch.update_pte.mmu_seq = vcpu->kvm->mmu_notifier_seq;
/* implicit mb(), we'll read before PT lock is unlocked */
smp_rmb();
pfn = gfn_to_pfn(vcpu->kvm, gfn);
up_read(&current->mm->mmap_sem);

if (is_error_pfn(pfn)) {
kvm_release_pfn_clean(pfn);
Expand Down
8 changes: 1 addition & 7 deletions arch/x86/kvm/paging_tmpl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -102,14 +102,10 @@ static bool FNAME(cmpxchg_gpte)(struct kvm *kvm,
pt_element_t *table;
struct page *page;

down_read(&current->mm->mmap_sem);
page = gfn_to_page(kvm, table_gfn);
up_read(&current->mm->mmap_sem);

table = kmap_atomic(page, KM_USER0);

ret = CMPXCHG(&table[index], orig_pte, new_pte);

kunmap_atomic(table, KM_USER0);

kvm_release_page_dirty(page);
Expand Down Expand Up @@ -418,7 +414,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
return 0;
}

down_read(&current->mm->mmap_sem);
if (walker.level == PT_DIRECTORY_LEVEL) {
gfn_t large_gfn;
large_gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE-1);
Expand All @@ -428,9 +423,8 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
}
}
mmu_seq = vcpu->kvm->mmu_notifier_seq;
/* implicit mb(), we'll read before PT lock is unlocked */
smp_rmb();
pfn = gfn_to_pfn(vcpu->kvm, walker.gfn);
up_read(&current->mm->mmap_sem);

/* mmio */
if (is_error_pfn(pfn)) {
Expand Down
4 changes: 0 additions & 4 deletions arch/x86/kvm/vmx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2010,9 +2010,7 @@ static int alloc_apic_access_page(struct kvm *kvm)
if (r)
goto out;

down_read(&current->mm->mmap_sem);
kvm->arch.apic_access_page = gfn_to_page(kvm, 0xfee00);
up_read(&current->mm->mmap_sem);
out:
up_write(&kvm->slots_lock);
return r;
Expand All @@ -2034,10 +2032,8 @@ static int alloc_identity_pagetable(struct kvm *kvm)
if (r)
goto out;

down_read(&current->mm->mmap_sem);
kvm->arch.ept_identity_pagetable = gfn_to_page(kvm,
VMX_EPT_IDENTITY_PAGETABLE_ADDR >> PAGE_SHIFT);
up_read(&current->mm->mmap_sem);
out:
up_write(&kvm->slots_lock);
return r;
Expand Down
6 changes: 0 additions & 6 deletions arch/x86/kvm/x86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -946,10 +946,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
/* ...but clean it before doing the actual write */
vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);

down_read(&current->mm->mmap_sem);
vcpu->arch.time_page =
gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);
up_read(&current->mm->mmap_sem);

if (is_error_page(vcpu->arch.time_page)) {
kvm_release_page_clean(vcpu->arch.time_page);
Expand Down Expand Up @@ -2322,9 +2320,7 @@ static int emulator_cmpxchg_emulated(unsigned long addr,

val = *(u64 *)new;

down_read(&current->mm->mmap_sem);
page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
up_read(&current->mm->mmap_sem);

kaddr = kmap_atomic(page, KM_USER0);
set_64bit((u64 *)(kaddr + offset_in_page(gpa)), val);
Expand Down Expand Up @@ -3089,9 +3085,7 @@ static void vapic_enter(struct kvm_vcpu *vcpu)
if (!apic || !apic->vapic_addr)
return;

down_read(&current->mm->mmap_sem);
page = gfn_to_page(vcpu->kvm, apic->vapic_addr >> PAGE_SHIFT);
up_read(&current->mm->mmap_sem);

vcpu->arch.apic->vapic_page = page;
}
Expand Down
10 changes: 5 additions & 5 deletions virt/kvm/kvm_main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -723,9 +723,6 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
}
EXPORT_SYMBOL_GPL(gfn_to_hva);

/*
* Requires current->mm->mmap_sem to be held
*/
pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
{
struct page *page[1];
Expand All @@ -741,20 +738,23 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
return page_to_pfn(bad_page);
}

npages = get_user_pages(current, current->mm, addr, 1, 1, 0, page,
NULL);
npages = get_user_pages_fast(addr, 1, 1, page);

if (unlikely(npages != 1)) {
struct vm_area_struct *vma;

down_read(&current->mm->mmap_sem);
vma = find_vma(current->mm, addr);

if (vma == NULL || addr < vma->vm_start ||
!(vma->vm_flags & VM_PFNMAP)) {
up_read(&current->mm->mmap_sem);
get_page(bad_page);
return page_to_pfn(bad_page);
}

pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
up_read(&current->mm->mmap_sem);
BUG_ON(!is_mmio_pfn(pfn));
} else
pfn = page_to_pfn(page[0]);
Expand Down

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