* Denis Plotnikov (dplotni...@virtuozzo.com) wrote:
> The patch set adds the ability to make external snapshots while VM is running.
cc'ing in Andrea since this uses sigsegv's to avoid userfault-wp that
isn't there yet.
Hi Denis,
How robust are you finding this SEGV based trick; for example what
about things like the kernel walking vhost queues or similar kernel
nasties?
Dave
> The workflow to make a snapshot is the following:
> 1. Pause the vm
> 2. Make a snapshot of block devices using the scheme of your choice
> 3. Turn on background-snapshot migration capability
> 4. Start the migration using the destination (migration stream) of your
> choice.
> The migration will resume the vm execution by itself
> when it has the devices' states saved and is ready to start ram writing
> to the migration stream.
> 5. Listen to the migration finish event
>
> The feature relies on KVM unapplied ability to report the faulting address.
> Please find the KVM patch snippet to make the patchset work below:
>
> +++ b/arch/x86/kvm/vmx.c
> @@ -XXXX,X +XXXX,XX @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
>
> vcpu->arch.exit_qualification = exit_qualification;
>
> - return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
> + r = kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
> + if (r == -EFAULT) {
> + unsigned long hva = kvm_vcpu_gfn_to_hva(vcpu, gpa >>
> PAGE_SHIFT);
> +
> + vcpu->run->exit_reason = KVM_EXIT_FAIL_MEM_ACCESS;
> + vcpu->run->hw.hardware_exit_reason =
> EXIT_REASON_EPT_VIOLATION;
> + vcpu->run->fail_mem_access.hva = hva | (gpa & (PAGE_SIZE-1));
> + r = 0;
> +
> + }
> + return r;
>
> The patch to KVM can be sent if the patch set approved
>
> Denis Plotnikov (7):
> migration: add background snapshot capability
> bitops: add some atomic versions of bitmap operations
> threads: add infrastructure to process sigsegv
> migration: add background snapshot infrastructure
> kvm: add failed memeory access exit reason
> kvm: add vCPU failed memeory access processing
> migration: add background snapshotting
>
> include/exec/ram_addr.h | 7 +
> include/exec/ramlist.h | 4 +-
> include/qemu/bitops.h | 24 +++
> include/qemu/thread.h | 5 +
> linux-headers/linux/kvm.h | 5 +
> migration/migration.c | 141 +++++++++++++++-
> migration/migration.h | 1 +
> migration/ram.c | 333 ++++++++++++++++++++++++++++++++++++--
> migration/ram.h | 11 +-
> migration/savevm.c | 91 ++++++-----
> migration/savevm.h | 2 +
> qapi/migration.json | 6 +-
> target/i386/kvm.c | 18 +++
> util/qemu-thread-posix.c | 50 ++++++
> 14 files changed, 635 insertions(+), 63 deletions(-)
>
> --
> 2.17.0
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
