On Thu, Jul 23, 2020 at 01:07:24PM -0700, Ram Pai wrote:
> From: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
>
> 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 call directly instead of triggering such a mechanism. This
> way kvmppc_uvmem_drop_pages() can be called even when hot unplugging a
> memslot.
>
> 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 held 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: Ram Pai <linuxram@xxxxxxxxxx>
> [modified the changelog description]
> 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 c772e92..daffa6e 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -632,35 +632,55 @@ 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;
> +
> + mmap_read_lock(kvm->mm);
> +
> + addr = slot->userspace_addr;
> + end = addr + (slot->npages * PAGE_SIZE);
>
> - for (i = free->npages; i; --i, ++gfn) {
> - struct page *uvmem_page;
> + gfn = slot->base_gfn;
> + for (i = slot->npages; i; --i, ++gfn, addr += PAGE_SIZE) {
> +
> + /* Fetch the VMA if addr is not in the latest fetched one */
> + if (!vma || (addr < vma->vm_start || addr >= vma->vm_end)) {
> + vma = find_vma_intersection(kvm->mm, addr, end);
> + if (!vma ||
> + vma->vm_start > addr || vma->vm_end < end) {
> + pr_err("Can't find VMA for gfn:0x%lx\n", gfn);
> + break;
> + }
There is a potential issue with the boundary condition check here
which I discussed with Laurent yesterday. Guess he hasn't gotten around
to look at it yet.
Regards,
Bharata.
