Re: [RFC 07/37] KVM: s390: protvirt: Secure memory is not mergeable

David Hildenbrand <david@xxxxxxxxxx> · Thu, 24 Oct 2019 18:49:19 +0200

On 24.10.19 18:33, Claudio Imbrenda wrote:
On Thu, 24 Oct 2019 18:07:14 +0200
David Hildenbrand <david@xxxxxxxxxx> wrote:

On 24.10.19 13:40, Janosch Frank wrote:
KSM will not work on secure pages, because when the kernel reads a
secure page, it will be encrypted and hence no two pages will look
the same.

Let's mark the guest pages as unmergeable when we transition to
secure mode.

Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
---
   arch/s390/include/asm/gmap.h |  1 +
   arch/s390/kvm/kvm-s390.c     |  6 ++++++
   arch/s390/mm/gmap.c          | 28 ++++++++++++++++++----------
   3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/arch/s390/include/asm/gmap.h
b/arch/s390/include/asm/gmap.h index 6efc0b501227..eab6a2ec3599
100644 --- a/arch/s390/include/asm/gmap.h
+++ b/arch/s390/include/asm/gmap.h
@@ -145,4 +145,5 @@ int gmap_mprotect_notify(struct gmap *,
unsigned long start,
   void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long
dirty_bitmap[4], unsigned long gaddr, unsigned long vmaddr);
+int gmap_mark_unmergeable(void);
   #endif /* _ASM_S390_GMAP_H */
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 924132d92782..d1ba12f857e7 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2176,6 +2176,12 @@ static int kvm_s390_handle_pv(struct kvm
*kvm, struct kvm_pv_cmd *cmd) if (r)
   			break;
   
+		down_write(&current->mm->mmap_sem);
+		r = gmap_mark_unmergeable();
+		up_write(&current->mm->mmap_sem);
+		if (r)
+			break;
+
   		mutex_lock(&kvm->lock);
   		kvm_s390_vcpu_block_all(kvm);
   		/* FMT 4 SIE needs esca */
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index edcdca97e85e..bf365a09f900 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -2548,6 +2548,23 @@ int s390_enable_sie(void)
   }
   EXPORT_SYMBOL_GPL(s390_enable_sie);
   
+int gmap_mark_unmergeable(void)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (ksm_madvise(vma, vma->vm_start, vma->vm_end,
+				MADV_UNMERGEABLE, &vma->vm_flags))
{
+			mm->context.uses_skeys = 0;

That skey setting does not make too much sense when coming via
kvm_s390_handle_pv(). handle that in the caller?

protected guests run keyless; any attempt to use keys in the guest will
result in an exception in the guest.

still, this is the recovery path for the "mm->context.uses_skeys = 1;" 
in enable_skey_walk_ops() and confuses reader (like me).


--

Thanks,

David / dhildenb








