s390/mm: add shadow gmap support

For a nested KVM guest the outer KVM host needs to create shadow
page tables for the nested guest. This patch adds the basic support
to the guest address space (gmap) code.

For each guest address space the inner KVM host creates, the first
outer KVM host needs to create shadow page tables. The address space
is identified by the ASCE loaded into the control register 1 at the
time the inner SIE instruction for the second nested KVM guest is
executed. The outer KVM host creates the shadow tables starting with
the table identified by the ASCE on a on-demand basis. The outer KVM
host will get repeated faults for all the shadow tables needed to
run the second KVM guest.

While a shadow page table for the second KVM guest is active the access
to the origin region, segment and page tables needs to be restricted
for the first KVM guest. For region and segment and page tables the first
KVM guest may read the memory, but write attempt has to lead to an
unshadow.  This is done using the page invalid and read-only bits in the
page table of the first KVM guest. If the first guest re-accesses one of
the origin pages of a shadow, it gets a fault and the affected parts of
the shadow page table hierarchy needs to be removed again.

PGSTE tables don't have to be shadowed, as all interpretation assist can't
deal with the invalid bits in the shadow pte being set differently than
the original ones provided by the first KVM guest.

Many bug fixes and improvements by David Hildenbrand.

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 35dde6afffcf..a6e7fc8f5b49 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -256,6 +256,7 @@ static inline int is_module_addr(void *addr)
 /* Bits in the region table entry */
 #define _REGION_ENTRY_ORIGIN    ~0xfffUL/* region/segment table origin      */
 #define _REGION_ENTRY_PROTECT   0x200   /* region protection bit            */
+#define _REGION_ENTRY_OFFSET    0xc0    /* region table offset              */
 #define _REGION_ENTRY_INVALID   0x20    /* invalid region table entry       */
 #define _REGION_ENTRY_TYPE_MASK 0x0c    /* region/segment table type mask   */
 #define _REGION_ENTRY_TYPE_R1   0x0c    /* region first table type          */
@@ -327,6 +328,7 @@ static inline int is_module_addr(void *addr)
 #define PGSTE_GC_BIT    0x0002000000000000UL
 #define PGSTE_UC_BIT    0x0000800000000000UL    /* user dirty (migration) */
 #define PGSTE_IN_BIT    0x0000400000000000UL    /* IPTE notify bit */
+#define PGSTE_VSIE_BIT  0x0000200000000000UL    /* ref'd in a shadow table */
 
 /* Guest Page State used for virtualization */
 #define _PGSTE_GPS_ZERO         0x0000000080000000UL
@@ -885,12 +887,16 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma,
 void ptep_set_pte_at(struct mm_struct *mm, unsigned long addr,
                      pte_t *ptep, pte_t entry);
 void ptep_set_notify(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
-void ptep_notify(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
+void ptep_notify(struct mm_struct *mm, unsigned long addr,
+                 pte_t *ptep, unsigned long bits);
 int ptep_force_prot(struct mm_struct *mm, unsigned long gaddr,
-                    pte_t *ptep, int prot);
+                    pte_t *ptep, int prot, unsigned long bit);
 void ptep_zap_unused(struct mm_struct *mm, unsigned long addr,
                      pte_t *ptep , int reset);
 void ptep_zap_key(struct mm_struct *mm, unsigned long addr, pte_t *ptep);
+int ptep_shadow_pte(struct mm_struct *mm, unsigned long saddr,
+                    pte_t *sptep, pte_t *tptep, int write);
+void ptep_unshadow_pte(struct mm_struct *mm, unsigned long saddr, pte_t *ptep);
 
 bool test_and_clear_guest_dirty(struct mm_struct *mm, unsigned long address);
 int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,