iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

KVM: Add generic support for dirty page logging

Browse Source 
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: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
This commit is contained in:
Mario Smarduch 2015-01-15 15:58:53 -08:00 committed by Christoffer Dall
parent a6d5101661
commit ba0513b5b8
3 changed files with 95 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
include/linux/kvm_host.h
View File

@ -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);

6
virt/kvm/Kconfig
View File

@ -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

80
virt/kvm/kvm_main.c
View File

@ -995,6 +995,86 @@ out:
}
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;