Currently qemu/kvm on s390 uses a guest mapping that does not
allow the guest backing page table to be write-protected to
support older systems. On those older systems a host write
protection fault will be delivered to the guest.
Newer systems allow to write-protect the guest backing memory
and let the fault be delivered to the host, thus allowing COW.
Use a capability bit to tell qemu if that is possible.
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Acked-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
---
arch/s390/include/asm/sclp.h | 1 +
arch/s390/kvm/kvm-s390.c | 4 ++++
drivers/s390/char/sclp_cmd.c | 12 +++++++++++-
include/linux/kvm.h | 1 +
4 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/arch/s390/include/asm/sclp.h b/arch/s390/include/asm/sclp.h
index fed7bee..bf238c5 100644
--- a/arch/s390/include/asm/sclp.h
+++ b/arch/s390/include/asm/sclp.h
@@ -48,6 +48,7 @@ int sclp_cpu_deconfigure(u8 cpu);
void sclp_facilities_detect(void);
unsigned long long sclp_get_rnmax(void);
unsigned long long sclp_get_rzm(void);
+u8 sclp_get_fac85(void);
int sclp_sdias_blk_count(void);
int sclp_sdias_copy(void *dest, int blk_num, int nr_blks);
int sclp_chp_configure(struct chp_id chpid);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e5e3800..5c761bf 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -28,6 +28,7 @@
#include <asm/pgtable.h>
#include <asm/nmi.h>
#include <asm/switch_to.h>
+#include <asm/sclp.h>
#include "kvm-s390.h"
#include "gaccess.h"
@@ -140,6 +141,9 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_MAX_VCPUS:
r = KVM_MAX_VCPUS;
break;
+ case KVM_CAP_S390_COW:
+ r = sclp_get_fac85() & 0x2;
+ break;
default:
r = 0;
}
diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
index 231a1d8..032171e 100644
--- a/drivers/s390/char/sclp_cmd.c
+++ b/drivers/s390/char/sclp_cmd.c
@@ -17,6 +17,7 @@
#include <linux/mm.h>
#include <linux/mmzone.h>
#include <linux/memory.h>
+#include <linux/module.h>
#include <linux/platform_device.h>
#include <asm/chpid.h>
#include <asm/sclp.h>
@@ -38,7 +39,8 @@ struct read_info_sccb {
u64 facilities; /* 48-55 */
u8 _reserved2[84 - 56]; /* 56-83 */
u8 fac84; /* 84 */
- u8 _reserved3[91 - 85]; /* 85-90 */
+ u8 fac85; /* 85 */
+ u8 _reserved3[91 - 86]; /* 86-90 */
u8 flags; /* 91 */
u8 _reserved4[100 - 92]; /* 92-99 */
u32 rnsize2; /* 100-103 */
@@ -51,6 +53,7 @@ static int __initdata early_read_info_sccb_valid;
u64 sclp_facilities;
static u8 sclp_fac84;
+static u8 sclp_fac85;
static unsigned long long rzm;
static unsigned long long rnmax;
@@ -112,6 +115,7 @@ void __init sclp_facilities_detect(void)
sccb = &early_read_info_sccb;
sclp_facilities = sccb->facilities;
sclp_fac84 = sccb->fac84;
+ sclp_fac85 = sccb->fac85;
rnmax = sccb->rnmax ? sccb->rnmax : sccb->rnmax2;
rzm = sccb->rnsize ? sccb->rnsize : sccb->rnsize2;
rzm <<= 20;
@@ -127,6 +131,12 @@ unsigned long long sclp_get_rzm(void)
return rzm;
}
+u8 sclp_get_fac85(void)
+{
+ return sclp_fac85;
+}
+EXPORT_SYMBOL_GPL(sclp_get_fac85);
+
/*
* This function will be called after sclp_facilities_detect(), which gets
* called from early.c code. Therefore the sccb should have valid contents.
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 8d696cf..09f2b3a 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -616,6 +616,7 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_KVMCLOCK_CTRL 76
#define KVM_CAP_SIGNAL_MSI 77
#define KVM_CAP_PPC_GET_SMMU_INFO 78
+#define KVM_CAP_S390_COW 79
#ifdef KVM_CAP_IRQ_ROUTING
--
1.7.10.2
--
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