[kvm-unit-tests PATCH 5/6] lib: s390x: Use a new asce for each PV guest

Janosch Frank
2022-07-29T08:28:27Z

Every PV guest needs its own ASCE so let's copy the topmost table
designated by CR1 to create a new ASCE for the PV guest. Before and
after SIE we now need to switch ASCEs to and from the PV guest / test
ASCE. The SIE assembly function does that automatically.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
lib/s390x/asm-offsets.c | 2 ++
lib/s390x/sie.c | 2 ++
lib/s390x/sie.h | 2 ++
lib/s390x/uv.c | 35 +++++++++++++++++++++++++++++++++--
lib/s390x/uv.h | 5 ++---
s390x/cpu.S | 6 ++++++
6 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/lib/s390x/asm-offsets.c b/lib/s390x/asm-offsets.c
index fbea3278..f612f327 100644
--- a/lib/s390x/asm-offsets.c
+++ b/lib/s390x/asm-offsets.c
@@ -75,9 +75,11 @@ int main(void)
OFFSET(SIE_SAVEAREA_HOST_GRS, vm_save_area, host.grs[0]);
OFFSET(SIE_SAVEAREA_HOST_FPRS, vm_save_area, host.fprs[0]);
OFFSET(SIE_SAVEAREA_HOST_FPC, vm_save_area, host.fpc);
+ OFFSET(SIE_SAVEAREA_HOST_ASCE, vm_save_area, host.asce);
OFFSET(SIE_SAVEAREA_GUEST_GRS, vm_save_area, guest.grs[0]);
OFFSET(SIE_SAVEAREA_GUEST_FPRS, vm_save_area, guest.fprs[0]);
OFFSET(SIE_SAVEAREA_GUEST_FPC, vm_save_area, guest.fpc);
+ OFFSET(SIE_SAVEAREA_GUEST_ASCE, vm_save_area, guest.asce);
OFFSET(STACK_FRAME_INT_BACKCHAIN, stack_frame_int, back_chain);
OFFSET(STACK_FRAME_INT_FPC, stack_frame_int, fpc);
OFFSET(STACK_FRAME_INT_FPRS, stack_frame_int, fprs);
diff --git a/lib/s390x/sie.c b/lib/s390x/sie.c
index c3a53ad6..5ba669f1 100644
--- a/lib/s390x/sie.c
+++ b/lib/s390x/sie.c
@@ -84,6 +84,8 @@ void sie_guest_create(struct vm *vm, uint64_t guest_mem, uint64_t guest_mem_len)

/* Guest memory chunks are always 1MB */
assert(!(guest_mem_len & ~HPAGE_MASK));
+ /* For non-PV guests we re-use the host's ASCE for ease of use */
+ vm->save_area.guest.asce = stctg(1);
/* Currently MSO/MSL is the easiest option */
vm->sblk->mso = (uint64_t)guest_mem;
vm->sblk->msl = (uint64_t)guest_mem + ((guest_mem_len - 1) & HPAGE_MASK);
diff --git a/lib/s390x/sie.h b/lib/s390x/sie.h
index 320c4218..3e3605c9 100644
--- a/lib/s390x/sie.h
+++ b/lib/s390x/sie.h
@@ -205,12 +205,14 @@ union {
struct vm_uv {
uint64_t vm_handle;
uint64_t vcpu_handle;
+ uint64_t asce;
void *conf_base_stor;
void *conf_var_stor;
void *cpu_stor;
};

struct vm_save_regs {
+ uint64_t asce;
uint64_t grs[16];
uint64_t fprs[16];
uint32_t fpc;
diff --git a/lib/s390x/uv.c b/lib/s390x/uv.c
index 3b4cafa9..99775929 100644
--- a/lib/s390x/uv.c
+++ b/lib/s390x/uv.c
@@ -76,7 +76,8 @@ void uv_init(void)
int cc;

/* Let's not do this twice */
- assert(!initialized);
+ if (initialized)
+ return;
/* Query is done on initialization but let's check anyway */
assert(uvcb_qui.header.rc == 1 || uvcb_qui.header.rc == 0x100);

@@ -90,6 +91,25 @@ void uv_init(void)
initialized = true;
}

+/*
+ * Create a new ASCE for the UV config because they can't be shared
+ * for security reasons. We just simply copy the top most table into a
+ * fresh set of allocated pages and use those pages as the asce.
+ */
+static uint64_t create_asce(void)
+{
+ void *pgd_new, *pgd_old;
+ uint64_t asce = stctg(1);
+
+ pgd_new = memalign_pages_flags(PAGE_SIZE, PAGE_SIZE * 4, 0);
+ pgd_old = (void *)(asce & PAGE_MASK);
+
+ memcpy(pgd_new, pgd_old, PAGE_SIZE * 4);
+
+ asce = __pa(pgd_new) | ASCE_DT_REGION1 | REGION_TABLE_LENGTH | ASCE_P;
+ return asce;
+}
+
void uv_create_guest(struct vm *vm)
{
struct uv_cb_cgc uvcb_cgc = {
@@ -125,7 +145,8 @@ void uv_create_guest(struct vm *vm)
vm->uv.cpu_stor = memalign_pages_flags(PAGE_SIZE, uvcb_qui.cpu_stor_len, 0);
uvcb_csc.stor_origin = (uint64_t)vm->uv.cpu_stor;

- uvcb_cgc.guest_asce = (uint64_t)stctg(1);
+ uvcb_cgc.guest_asce = create_asce();
+ vm->save_area.guest.asce = uvcb_cgc.guest_asce;
uvcb_cgc.guest_sca = (uint64_t)vm->sca;

cc = uv_call(0, (uint64_t)&uvcb_cgc);
@@ -166,6 +187,16 @@ void uv_destroy_guest(struct vm *vm)
assert(cc == 0);
free_pages(vm->uv.conf_base_stor);
free_pages(vm->uv.conf_var_stor);
+
+ free_pages((void *)(vm->uv.asce & PAGE_MASK));
+ memset(&vm->uv, 0, sizeof(vm->uv));
+
+ /* Convert the sblk back to non-PV */
+ vm->save_area.guest.asce = stctg(1);
+ vm->sblk->sdf = 0;
+ vm->sblk->sidad = 0;
+ vm->sblk->pv_handle_cpu = 0;
+ vm->sblk->pv_handle_config = 0;
}

int uv_unpack(struct vm *vm, uint64_t addr, uint64_t len, uint64_t tweak)
diff --git a/lib/s390x/uv.h b/lib/s390x/uv.h
index 44264861..5fe29bda 100644
--- a/lib/s390x/uv.h
+++ b/lib/s390x/uv.h
@@ -28,9 +28,8 @@ static inline void uv_setup_asces(void)
/* We need to have a valid primary ASCE to run guests. */
setup_vm();

- /* Set P bit in ASCE as it is required for PV guests */
- asce = stctg(1) | ASCE_P;
- lctlg(1, asce);
+ /* Grab the ASCE which setup_vm() just set up */
+ asce = stctg(1);

/* Copy ASCE into home space CR */
lctlg(13, asce);
diff --git a/s390x/cpu.S b/s390x/cpu.S
index 82b5e25d..45bd551a 100644
--- a/s390x/cpu.S
+++ b/s390x/cpu.S
@@ -76,6 +76,9 @@ sie64a:
.endr
stfpc SIE_SAVEAREA_HOST_FPC(%r3)

+ stctg %c1, %c1, SIE_SAVEAREA_HOST_ASCE(%r3)
+ lctlg %c1, %c1, SIE_SAVEAREA_GUEST_ASCE(%r3)
+
# Store scb and save_area pointer into stack frame
stg %r2,__SF_SIE_CONTROL(%r15) # save control block pointer
stg %r3,__SF_SIE_SAVEAREA(%r15) # save guest register save area
@@ -102,6 +105,9 @@ sie_exit:
# Load guest register save area
lg %r14,__SF_SIE_SAVEAREA(%r15)

+ # Restore the host asce
+ lctlg %c1, %c1, SIE_SAVEAREA_HOST_ASCE(%r14)
+
# Store guest's gprs, fprs and fpc
stmg %r0,%r13,SIE_SAVEAREA_GUEST_GRS(%r14) # save guest gprs 0-13
.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
--
2.34.1