iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86/xen: allow nesting of same lazy mode

Browse Source 
When running as a paravirtualized guest under Xen, Linux is using
"lazy mode" for issuing hypercalls which don't need to take immediate
effect in order to improve performance (examples are e.g. multiple
PTE changes).

There are two different lazy modes defined: MMU and CPU lazy mode.
Today it is not possible to nest multiple lazy mode sections, even if
they are of the same kind. A recent change in memory management added
nesting of MMU lazy mode sections, resulting in a regression when
running as Xen PV guest.

Technically there is no reason why nesting of multiple sections of the
same kind of lazy mode shouldn't be allowed. So add support for that
for fixing the regression.

Fixes: bcc6cc8325 ("mm: add default definition of set_ptes()")
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20230913113828.18421-4-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Juergen Gross 2023-09-13 13:38:28 +02:00
parent a4a7644c15
commit 49147beb0c
2 changed files with 14 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
arch/x86/include/asm/xen/hypervisor.h
View File

@ -72,10 +72,18 @@ enum xen_lazy_mode {
};
DECLARE_PER_CPU(enum xen_lazy_mode, xen_lazy_mode);
DECLARE_PER_CPU(unsigned int, xen_lazy_nesting);
static inline void enter_lazy(enum xen_lazy_mode mode)
{
BUG_ON(this_cpu_read(xen_lazy_mode) != XEN_LAZY_NONE);
enum xen_lazy_mode old_mode = this_cpu_read(xen_lazy_mode);
if (mode == old_mode) {
this_cpu_inc(xen_lazy_nesting);
return;
}
BUG_ON(old_mode != XEN_LAZY_NONE);
this_cpu_write(xen_lazy_mode, mode);
}
@ -84,7 +92,10 @@ static inline void leave_lazy(enum xen_lazy_mode mode)
{
BUG_ON(this_cpu_read(xen_lazy_mode) != mode);
this_cpu_write(xen_lazy_mode, XEN_LAZY_NONE);
if (this_cpu_read(xen_lazy_nesting) == 0)
this_cpu_write(xen_lazy_mode, XEN_LAZY_NONE);
else
this_cpu_dec(xen_lazy_nesting);
}
enum xen_lazy_mode xen_get_lazy_mode(void);

1
arch/x86/xen/enlighten_pv.c
View File

@ -102,6 +102,7 @@ struct tls_descs {
};
DEFINE_PER_CPU(enum xen_lazy_mode, xen_lazy_mode) = XEN_LAZY_NONE;
DEFINE_PER_CPU(unsigned int, xen_lazy_nesting);
enum xen_lazy_mode xen_get_lazy_mode(void)
{