On Tue, Jul 21, 2020 at 12:42:02PM +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.
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 5a4b02d3f651..ba5c7c77cc3a 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -624,35 +624,55 @@ 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;
We typically use gfn_to_hva() for that, but that won't work for a
memslot that is already marked INVALID which is the case here.
I think it is ok to access slot->userspace_addr here of an INVALID
memslot, but just thought of explictly bringing this up.
+ 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;
+ }
+ }
In Ram's series, kvmppc_memslot_page_merge() also walks the VMAs spanning
the memslot, but it uses a different logic for the same. Why can't these
two cases use the same method to walk the VMAs? Is there anything subtly
different between the two cases?