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KVM: s390: add capability indicating COW support

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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 <[email protected]>
Acked-by: Heiko Carstens <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>
This commit is contained in:
Christian Borntraeger 2012-05-15 14:15:25 +02:00 • committed by Marcelo Tosatti
commit 1526bf9ccf
4 changed files with 17 additions and 1 deletions
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12
drivers/s390/char/sclp_cmd.c
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@ -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.