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Commit ba0513b5 authored by Mario Smarduch's avatar Mario Smarduch Committed by Christoffer Dall
Browse files

KVM: Add generic support for dirty page logging 



kvm_get_dirty_log() provides generic handling of dirty bitmap, currently reused
by several architectures. Building on that we intrdoduce
kvm_get_dirty_log_protect() adding write protection to mark these pages dirty
for future write access, before next KVM_GET_DIRTY_LOG ioctl call from user
space.

Reviewed-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: default avatarMario Smarduch <m.smarduch@samsung.com>
parent a6d51016

include/linux/kvm_host.h

+9 −0
Original line number Diff line number Diff line
@@ -611,6 +611,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext); 


int kvm_get_dirty_log(struct kvm *kvm,

			struct kvm_dirty_log *log, int *is_dirty);



int kvm_get_dirty_log_protect(struct kvm *kvm,

			struct kvm_dirty_log *log, bool *is_dirty);



void kvm_arch_mmu_write_protect_pt_masked(struct kvm *kvm,

					struct kvm_memory_slot *slot,

					gfn_t gfn_offset,

					unsigned long mask);



int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,

				struct kvm_dirty_log *log);

virt/kvm/Kconfig

+6 −0
Original line number Diff line number Diff line
@@ -40,3 +40,9 @@ config KVM_VFIO 


config HAVE_KVM_ARCH_TLB_FLUSH_ALL

       bool



config HAVE_KVM_ARCH_DIRTY_LOG_PROTECT

       bool



config KVM_GENERIC_DIRTYLOG_READ_PROTECT

       bool

virt/kvm/kvm_main.c

+80 −0
Original line number Diff line number Diff line
@@ -995,6 +995,86 @@ int kvm_get_dirty_log(struct kvm *kvm, 
}

EXPORT_SYMBOL_GPL(kvm_get_dirty_log);



#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT

/**

 * kvm_get_dirty_log_protect - get a snapshot of dirty pages, and if any pages

 *	are dirty write protect them for next write.

 * @kvm:	pointer to kvm instance

 * @log:	slot id and address to which we copy the log

 * @is_dirty:	flag set if any page is dirty

 *

 * We need to keep it in mind that VCPU threads can write to the bitmap

 * concurrently. So, to avoid losing track of dirty pages we keep the

 * following order:

 *

 *    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. Upon return caller flushes TLB's if needed.

 *

 * 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_get_dirty_log_protect(struct kvm *kvm,

			struct kvm_dirty_log *log, bool *is_dirty)

{

	struct kvm_memory_slot *memslot;

	int r, i;

	unsigned long n;

	unsigned long *dirty_bitmap;

	unsigned long *dirty_bitmap_buffer;



	r = -EINVAL;

	if (log->slot >= KVM_USER_MEM_SLOTS)

		goto out;



	memslot = id_to_memslot(kvm->memslots, log->slot);



	dirty_bitmap = memslot->dirty_bitmap;

	r = -ENOENT;

	if (!dirty_bitmap)

		goto out;



	n = kvm_dirty_bitmap_bytes(memslot);



	dirty_bitmap_buffer = dirty_bitmap + n / sizeof(long);

	memset(dirty_bitmap_buffer, 0, n);



	spin_lock(&kvm->mmu_lock);

	*is_dirty = false;

	for (i = 0; i < n / sizeof(long); i++) {

		unsigned long mask;

		gfn_t offset;



		if (!dirty_bitmap[i])

			continue;



		*is_dirty = true;



		mask = xchg(&dirty_bitmap[i], 0);

		dirty_bitmap_buffer[i] = mask;



		offset = i * BITS_PER_LONG;

		kvm_arch_mmu_write_protect_pt_masked(kvm, memslot, offset,

								mask);

	}



	spin_unlock(&kvm->mmu_lock);



	r = -EFAULT;

	if (copy_to_user(log->dirty_bitmap, dirty_bitmap_buffer, n))

		goto out;



	r = 0;

out:

	return r;

}

EXPORT_SYMBOL_GPL(kvm_get_dirty_log_protect);

#endif



bool kvm_largepages_enabled(void)

{

	return largepages_enabled;