On 11/22/2014 11:40 AM, Christoffer Dall wrote:
> On Thu, Nov 13, 2014 at 05:57:47PM -0800, Mario Smarduch wrote:
>> Add support to track dirty pages between user space KVM_GET_DIRTY_LOG ioctl
>> calls. We call kvm_get_dirty_log_protect() function to do most of the work.
>>
>> Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> Signed-off-by: Mario Smarduch <m.smarduch@xxxxxxxxxxx>
>> ---
>> arch/arm/kvm/Kconfig | 1 +
>> arch/arm/kvm/arm.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>> arch/arm/kvm/mmu.c | 22 ++++++++++++++++++++++
>> 3 files changed, 69 insertions(+)
>>
>> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
>> index f27f336..a8d1ace 100644
>> --- a/arch/arm/kvm/Kconfig
>> +++ b/arch/arm/kvm/Kconfig
>> @@ -24,6 +24,7 @@ config KVM
>> select HAVE_KVM_ARCH_TLB_FLUSH_ALL
>> select KVM_MMIO
>> select KVM_ARM_HOST
>> + select KVM_GENERIC_DIRTYLOG_READ_PROTECT
>> depends on ARM_VIRT_EXT && ARM_LPAE
>> ---help---
>> Support hosting virtualized guest machines. You will also
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index a99e0cd..040c0f3 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -737,9 +737,55 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>> }
>> }
>>
>> +/**
>> + * kvm_vm_ioctl_get_dirty_log - get and clear the log of dirty pages in a slot
>> + * @kvm: kvm instance
>> + * @log: slot id and address to which we copy the log
>> + *
>> + * We need to keep it in mind that VCPU threads can write to the bitmap
>> + * concurrently. So, to avoid losing data, we keep the following order for
>> + * each bit:
>> + *
>> + * 1. Take a snapshot of the bit and clear it if needed.
>> + * 2. Write protect the corresponding page.
>> + * 3. Copy the snapshot to the userspace.
>> + * 4. Flush TLB's if needed.
>> + *
>> + * Steps 1,2,3 are handled by kvm_get_dirty_log_protect().
>> + * Between 2 and 4, the guest may write to the page using the remaining TLB
>> + * entry. This is not a problem because the page is reported dirty using
>> + * the snapshot taken before and step 4 ensures that writes done after
>> + * exiting to userspace will be logged for the next call.
>> + */
>> int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log)
>> {
>> +#ifdef CONFIG_ARM
>> + int r;
>> + bool is_dirty = false;
>> +
>> + mutex_lock(&kvm->slots_lock);
>> +
>> + r = kvm_get_dirty_log_protect(kvm, log, &is_dirty);
>> + if (r)
>> + goto out;
>> +
>> + /*
>> + * kvm_get_dirty_log_protect() may fail and we may skip TLB flush
>> + * leaving few stale spte TLB entries which is harmless, given we're
>> + * just write protecting spte's, so few stale TLB's will be left in
>> + * original R/W state. And since the bitmap is corrupt userspace will
>> + * error out anyway (i.e. during migration or dirty page loging for
>
> s/loging/logging/
>
> Hmmm, where is this behavior specified in the ABI? If you call
> KVM_GET_DIRTY_LOG subsequently, you will now potentially have unreported
> dirty pages, which can be completely avoided by removing the
> if-statement and the goto above. Why not simply do that and get rid of
> this comment?
Yeah that makes sense, the comment is an overkill for these few lines.
>
>> + * other reasons) terminating dirty page logging.
>> + */
>> + if (is_dirty)
>> + kvm_flush_remote_tlbs(kvm);
>> +out:
>> + mutex_unlock(&kvm->slots_lock);
>> +
>> + return r;
>> +#else /* ARM64 */
>> return -EINVAL;
>> +#endif
>> }
>>
>> static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm,
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 1e8b6a9..8137455 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -870,6 +870,28 @@ void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
>> spin_unlock(&kvm->mmu_lock);
>> kvm_flush_remote_tlbs(kvm);
>> }
>> +
>> +/**
>> + * kvm_arch_mmu_write_protect_pt_masked() - write protect dirty pages
>> + * @kvm: The KVM pointer
>> + * @slot: The memory slot associated with mask
>> + * @gfn_offset: The gfn offset in memory slot
>> + * @mask: The mask of dirty pages at offset 'gfn_offset' in this memory
>> + * slot to be write protected
>> + *
>> + * Walks bits set in mask write protects the associated pte's. Caller must
>> + * acquire kvm_mmu_lock.
>> + */
>> +void kvm_arch_mmu_write_protect_pt_masked(struct kvm *kvm,
>> + struct kvm_memory_slot *slot,
>> + gfn_t gfn_offset, unsigned long mask)
>> +{
>> + phys_addr_t base_gfn = slot->base_gfn + gfn_offset;
>> + phys_addr_t start = (base_gfn + __ffs(mask)) << PAGE_SHIFT;
>> + phys_addr_t end = (base_gfn + __fls(mask) + 1) << PAGE_SHIFT;
>> +
>> + stage2_wp_range(kvm, start, end);
>> +}
>> #endif
>>
>> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> --
>> 1.7.9.5
>>
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