Laurent Dufour <ldufour@xxxxxxxxxxxxx> writes:
> Le 08/07/2020 à 13:25, Bharata B Rao a écrit :
>> On Fri, Jul 03, 2020 at 05:59:14PM +0200, Laurent Dufour wrote:
>>> When a secure memslot is dropped, all the pages backed in the secure device
>>> (aka really backed by secure memory by the Ultravisor) should be paged out
>>> to a normal page. Previously, this was achieved by triggering the page
>>> fault mechanism which is calling kvmppc_svm_page_out() on each pages.
>>>
>>> This can't work when hot unplugging a memory slot because the memory slot
>>> is flagged as invalid and gfn_to_pfn() is then not trying to access the
>>> page, so the page fault mechanism is not triggered.
>>>
>>> Since the final goal is to make a call to kvmppc_svm_page_out() it seems
>>> simpler to directly calling it instead of triggering such a mechanism. This
>>> way kvmppc_uvmem_drop_pages() can be called even when hot unplugging a
>>> memslot.
>>
>> Yes, this appears much simpler.
>
> Thanks Bharata for reviewing this.
>
>>
>>>
>>> Since kvmppc_uvmem_drop_pages() is already holding kvm->arch.uvmem_lock,
>>> the call to __kvmppc_svm_page_out() is made.
>>> As __kvmppc_svm_page_out needs the vma pointer to migrate the pages, the
>>> VMA is fetched in a lazy way, to not trigger find_vma() all the time. In
>>> addition, the mmap_sem is help in read mode during that time, not in write
>>> mode since the virual memory layout is not impacted, and
>>> kvm->arch.uvmem_lock prevents concurrent operation on the secure device.
>>>
>>> Cc: Ram Pai <linuxram@xxxxxxxxxx>
>>> Cc: Bharata B Rao <bharata@xxxxxxxxxxxxx>
>>> Cc: Paul Mackerras <paulus@xxxxxxxxxx>
>>> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
>>> ---
>>> arch/powerpc/kvm/book3s_hv_uvmem.c | 54 ++++++++++++++++++++----------
>>> 1 file changed, 37 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
>>> index 852cc9ae6a0b..479ddf16d18c 100644
>>> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
>>> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
>>> @@ -533,35 +533,55 @@ static inline int kvmppc_svm_page_out(struct vm_area_struct *vma,
>>> * fault on them, do fault time migration to replace the device PTEs in
>>> * QEMU page table with normal PTEs from newly allocated pages.
>>> */
>>> -void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
>>> +void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *slot,
>>> struct kvm *kvm, bool skip_page_out)
>>> {
>>> int i;
>>> struct kvmppc_uvmem_page_pvt *pvt;
>>> - unsigned long pfn, uvmem_pfn;
>>> - unsigned long gfn = free->base_gfn;
>>> + struct page *uvmem_page;
>>> + struct vm_area_struct *vma = NULL;
>>> + unsigned long uvmem_pfn, gfn;
>>> + unsigned long addr, end;
>>> +
>>> + down_read(&kvm->mm->mmap_sem);
>>
>> You should be using mmap_read_lock(kvm->mm) with recent kernels.
>
> Absolutely, shame on me, I reviewed Michel's series about that!
>
> Paul, Michael, could you fix that when pulling this patch or should I sent a
> whole new series?
Paul will take this series, so up to him.
cheers
