[S390] kvm: fix address mode switching

598841ca9919d008b520114d8a4378c4ce4e40a1 ([S390] use gmap address
spaces for kvm guest images) changed kvm to use a separate address
space for kvm guests. This address space was switched in __vcpu_run
In some cases (preemption, page fault) there is the possibility that
this address space switch is lost.
The typical symptom was a huge amount of validity intercepts or
random guest addressing exceptions.
Fix this by doing the switch in sie_loop and sie_exit and saving the
address space in the gmap structure itself. Also use the preempt
notifier.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

5 files changed, 15 insertions, 10 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 519eb5f187ef..c0cb794bb365 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -658,12 +658,14 @@ static inline void pgste_set_pte(pte_t *ptep, pgste_t pgste)
  * struct gmap_struct - guest address space
  * @mm: pointer to the parent mm_struct
  * @table: pointer to the page directory
+ * @asce: address space control element for gmap page table
  * @crst_list: list of all crst tables used in the guest address space
  */
 struct gmap {
         struct list_head list;
         struct mm_struct *mm;
         unsigned long *table;
+        unsigned long asce;
         struct list_head crst_list;
 };
 
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 532fd4322156..2b45591e1582 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -10,6 +10,7 @@
 #include <linux/sched.h>
 #include <asm/vdso.h>
 #include <asm/sigp.h>
+#include <asm/pgtable.h>
 
 /*
  * Make sure that the compiler is new enough. We want a compiler that
@@ -126,6 +127,7 @@ int main(void)
         DEFINE(__LC_KERNEL_STACK, offsetof(struct _lowcore, kernel_stack));
         DEFINE(__LC_ASYNC_STACK, offsetof(struct _lowcore, async_stack));
         DEFINE(__LC_PANIC_STACK, offsetof(struct _lowcore, panic_stack));
+        DEFINE(__LC_USER_ASCE, offsetof(struct _lowcore, user_asce));
         DEFINE(__LC_INT_CLOCK, offsetof(struct _lowcore, int_clock));
         DEFINE(__LC_MCCK_CLOCK, offsetof(struct _lowcore, mcck_clock));
         DEFINE(__LC_MACHINE_FLAGS, offsetof(struct _lowcore, machine_flags));
@@ -151,6 +153,7 @@ int main(void)
         DEFINE(__LC_VDSO_PER_CPU, offsetof(struct _lowcore, vdso_per_cpu_data));
         DEFINE(__LC_GMAP, offsetof(struct _lowcore, gmap));
         DEFINE(__LC_CMF_HPP, offsetof(struct _lowcore, cmf_hpp));
+        DEFINE(__GMAP_ASCE, offsetof(struct gmap, asce));
 #endif /* CONFIG_32BIT */
         return 0;
 }
diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 5f729d627cef..713da0760538 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -1076,6 +1076,11 @@ sie_loop:
         lg      %r14,__LC_THREAD_INFO           # pointer thread_info struct
         tm      __TI_flags+7(%r14),_TIF_EXIT_SIE
         jnz     sie_exit
+        lg      %r14,__LC_GMAP                  # get gmap pointer
+        ltgr    %r14,%r14
+        jz      sie_gmap
+        lctlg   %c1,%c1,__GMAP_ASCE(%r14)       # load primary asce
+sie_gmap:
         lg      %r14,__SF_EMPTY(%r15)           # get control block pointer
         SPP     __SF_EMPTY(%r15)                # set guest id
         sie     0(%r14)
@@ -1083,6 +1088,7 @@ sie_done:
         SPP     __LC_CMF_HPP                    # set host id
         lg      %r14,__LC_THREAD_INFO           # pointer thread_info struct
 sie_exit:
+        lctlg   %c1,%c1,__LC_USER_ASCE          # load primary asce
         ni      __TI_flags+6(%r14),255-(_TIF_SIE>>8)
         lg      %r14,__SF_EMPTY+8(%r15)         # load guest register save area
         stmg    %r0,%r13,0(%r14)                # save guest gprs 0-13
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index f17296e4fc89..b4eced131e5c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -263,10 +263,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
         vcpu->arch.guest_fpregs.fpc &= FPC_VALID_MASK;
         restore_fp_regs(&vcpu->arch.guest_fpregs);
         restore_access_regs(vcpu->arch.guest_acrs);
+        gmap_enable(vcpu->arch.gmap);
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
+        gmap_disable(vcpu->arch.gmap);
         save_fp_regs(&vcpu->arch.guest_fpregs);
         save_access_regs(vcpu->arch.guest_acrs);
         restore_fp_regs(&vcpu->arch.host_fpregs);
@@ -461,7 +463,6 @@ static void __vcpu_run(struct kvm_vcpu *vcpu)
         local_irq_disable();
         kvm_guest_enter();
         local_irq_enable();
-        gmap_enable(vcpu->arch.gmap);
         VCPU_EVENT(vcpu, 6, "entering sie flags %x",
                    atomic_read(&vcpu->arch.sie_block->cpuflags));
         if (sie64a(vcpu->arch.sie_block, vcpu->arch.guest_gprs)) {
@@ -470,7 +471,6 @@ static void __vcpu_run(struct kvm_vcpu *vcpu)
         }
         VCPU_EVENT(vcpu, 6, "exit sie icptcode %d",
                    vcpu->arch.sie_block->icptcode);
-        gmap_disable(vcpu->arch.gmap);
         local_irq_disable();
         kvm_guest_exit();
         local_irq_enable();
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 4d1f2bce87b3..f69ff3c13496 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -160,6 +160,8 @@ struct gmap *gmap_alloc(struct mm_struct *mm)
         table = (unsigned long *) page_to_phys(page);
         crst_table_init(table, _REGION1_ENTRY_EMPTY);
         gmap->table = table;
+        gmap->asce = _ASCE_TYPE_REGION1 | _ASCE_TABLE_LENGTH |
+                     _ASCE_USER_BITS | __pa(table);
         list_add(&gmap->list, &mm->context.gmap_list);
         return gmap;
 
@@ -240,10 +242,6 @@ EXPORT_SYMBOL_GPL(gmap_free);
  */
 void gmap_enable(struct gmap *gmap)
 {
-        /* Load primary space page table origin. */
-        S390_lowcore.user_asce = _ASCE_TYPE_REGION1 | _ASCE_TABLE_LENGTH |
-                                 _ASCE_USER_BITS | __pa(gmap->table);
-        asm volatile("lctlg 1,1,%0\n" : : "m" (S390_lowcore.user_asce) );
         S390_lowcore.gmap = (unsigned long) gmap;
 }
 EXPORT_SYMBOL_GPL(gmap_enable);
@@ -254,10 +252,6 @@ EXPORT_SYMBOL_GPL(gmap_enable);
  */
 void gmap_disable(struct gmap *gmap)
 {
-        /* Load primary space page table origin. */
-        S390_lowcore.user_asce =
-                gmap->mm->context.asce_bits | __pa(gmap->mm->pgd);
-        asm volatile("lctlg 1,1,%0\n" : : "m" (S390_lowcore.user_asce) );
         S390_lowcore.gmap = 0UL;
 }
 EXPORT_SYMBOL_GPL(gmap_disable);