KVM: PPC: Book3S HV: Rework secure mem slot dropping

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.

Reviewed-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
        [modified check on the VMA in kvmppc_uvmem_drop_pages]
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
	[modified the changelog description]
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 565f24b..0d49e34 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -594,35 +594,53 @@ 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;
+
+       mmap_read_lock(kvm->mm);
+
+       addr = slot->userspace_addr;
 
-       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_end) {
+                       vma = find_vma_intersection(kvm->mm, addr, addr+1);
+                       if (!vma) {
+                               pr_err("Can't find VMA for gfn:0x%lx\n", gfn);
+                               break;
+                       }
+               }
 
                mutex_lock(&kvm->arch.uvmem_lock);
-               if (!kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) {
+
+               if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) {
+                       uvmem_page = pfn_to_page(uvmem_pfn);
+                       pvt = uvmem_page->zone_device_data;
+                       pvt->skip_page_out = skip_page_out;
+                       pvt->remove_gfn = true;
+
+                       if (__kvmppc_svm_page_out(vma, addr, addr + PAGE_SIZE,
+                                                 PAGE_SHIFT, kvm, pvt->gpa))
+                               pr_err("Can't page out gpa:0x%lx addr:0x%lx\n",
+                                      pvt->gpa, addr);
+               } else {
+                       /* Remove the shared flag if any */
                        kvmppc_gfn_remove(gfn, kvm);
-                       mutex_unlock(&kvm->arch.uvmem_lock);
-                       continue;
                }
 
-               uvmem_page = pfn_to_page(uvmem_pfn);
-               pvt = uvmem_page->zone_device_data;
-               pvt->skip_page_out = skip_page_out;
-               pvt->remove_gfn = true;
                mutex_unlock(&kvm->arch.uvmem_lock);
-
-               pfn = gfn_to_pfn(kvm, gfn);
-               if (is_error_noslot_pfn(pfn))
-                       continue;
-               kvm_release_pfn_clean(pfn);
        }
+
+       mmap_read_unlock(kvm->mm);
 }
 
 unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)