On 10/06/2010 12:52 PM, Gleb Natapov wrote:
On Wed, Oct 06, 2010 at 12:50:01PM +0200, Avi Kivity wrote:
> On 10/05/2010 04:59 PM, Marcelo Tosatti wrote:
> >On Mon, Oct 04, 2010 at 05:56:24PM +0200, Gleb Natapov wrote:
> >> If a guest accesses swapped out memory do not swap it in from vcpu thread
> >> context. Schedule work to do swapping and put vcpu into halted state
> >> instead.
> >>
> >> Interrupts will still be delivered to the guest and if interrupt will
> >> cause reschedule guest will continue to run another task.
> >>
> >> Signed-off-by: Gleb Natapov<gleb@xxxxxxxxxx>
> >> ---
> >> arch/x86/include/asm/kvm_host.h | 17 +++
> >> arch/x86/kvm/Kconfig | 1 +
> >> arch/x86/kvm/Makefile | 1 +
> >> arch/x86/kvm/mmu.c | 51 +++++++++-
> >> arch/x86/kvm/paging_tmpl.h | 4 +-
> >> arch/x86/kvm/x86.c | 109 +++++++++++++++++++-
> >> include/linux/kvm_host.h | 31 ++++++
> >> include/trace/events/kvm.h | 88 ++++++++++++++++
> >> virt/kvm/Kconfig | 3 +
> >> virt/kvm/async_pf.c | 220 +++++++++++++++++++++++++++++++++++++++
> >> virt/kvm/async_pf.h | 36 +++++++
> >> virt/kvm/kvm_main.c | 57 ++++++++--
> >> 12 files changed, 603 insertions(+), 15 deletions(-)
> >> create mode 100644 virt/kvm/async_pf.c
> >> create mode 100644 virt/kvm/async_pf.h
> >>
> >
> >> + async_pf_cache = NULL;
> >> +}
> >> +
> >> +void kvm_async_pf_vcpu_init(struct kvm_vcpu *vcpu)
> >> +{
> >> + INIT_LIST_HEAD(&vcpu->async_pf.done);
> >> + INIT_LIST_HEAD(&vcpu->async_pf.queue);
> >> + spin_lock_init(&vcpu->async_pf.lock);
> >> +}
> >> +
> >> +static void async_pf_execute(struct work_struct *work)
> >> +{
> >> + struct page *page;
> >> + struct kvm_async_pf *apf =
> >> + container_of(work, struct kvm_async_pf, work);
> >> + struct mm_struct *mm = apf->mm;
> >> + struct kvm_vcpu *vcpu = apf->vcpu;
> >> + unsigned long addr = apf->addr;
> >> + gva_t gva = apf->gva;
> >> +
> >> + might_sleep();
> >> +
> >> + use_mm(mm);
> >> + down_read(&mm->mmap_sem);
> >> + get_user_pages(current, mm, addr, 1, 1, 0,&page, NULL);
> >> + up_read(&mm->mmap_sem);
> >> + unuse_mm(mm);
> >> +
> >> + spin_lock(&vcpu->async_pf.lock);
> >> + list_add_tail(&apf->link,&vcpu->async_pf.done);
> >> + apf->page = page;
> >> + spin_unlock(&vcpu->async_pf.lock);
> >
> >This can fail, and apf->page become NULL.
>
> Does it even become NULL? On error, get_user_pages() won't update
> the pages argument, so page becomes garbage here.
>
apf is allocated with kmem_cache_zalloc() and ->page is set to NULL in
kvm_setup_async_pf() to be extra sure.
But you assign apf->page = page;, overriding it with garbage here.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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