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KVM: Avoid useless memory write when possible

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When writing to normal memory and the memory area is unchanged the write
can be safely skipped, avoiding the costly kvm_mmu_pte_write.

Signed-Off-By: Luca Tettamanti <kronos.it@gmail.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Luca Tettamanti 2007-06-19 22:41:38 +02:00 committed by Avi Kivity
parent 02c03a326a
commit a3c870bdce
1 changed files with 4 additions and 2 deletions
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6
drivers/kvm/kvm_main.c
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@ -1170,8 +1170,10 @@ static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
return 0; return 0;
mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT); mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT);
virt = kmap_atomic(page, KM_USER0); virt = kmap_atomic(page, KM_USER0);
kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes); if (memcmp(virt + offset_in_page(gpa), val, bytes)) {
memcpy(virt + offset_in_page(gpa), val, bytes); kvm_mmu_pte_write(vcpu, gpa, virt + offset, val, bytes);
memcpy(virt + offset_in_page(gpa), val, bytes);
}
kunmap_atomic(virt, KM_USER0); kunmap_atomic(virt, KM_USER0);
return 1; return 1;
} }