[Xen-devel] [PATCH] tools/libxc: Construct 32bit PV guests with L3 A/D bits set

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

With the 32 PAE build of Xen gone, 32bit PV guests' top level pagetables no
longer behave exactly like PAE in hardware.

They should have A/D bits set, for the same performance reasons as apply to
other levels.  This brings the domain builder in line with how Xen constructs
a 32bit dom0.

As a purely code improvement, make use of range notation to initialise
identical values in adjacent array elements.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Ian Jackson <Ian.Jackson@xxxxxxxxxx>

It turns out that neither Xen nor libxc sets dirty bits on L1 pagetables, but
I can't spot any documented reason for this.  My best guess is to avoid having
D/RO mappings of pagetables, but this isn't going to trip up a PV guest to
begin with.  Thoughts on reducing the performance cost there as well?
---
 tools/libxc/xc_dom_x86.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index 1897decedb..425b129146 100644
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -277,8 +277,8 @@ static int alloc_pgtables_x86_32_pae(struct xc_dom_image 
*dom)
         .levels = PGTBL_LEVELS_I386,
         .vaddr_mask = bits_to_mask(VIRT_BITS_I386),
         .lvl_prot[0] = _PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED,
-        .lvl_prot[1] = 
_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER,
-        .lvl_prot[2] = _PAGE_PRESENT,
+        .lvl_prot[1 ... 2] =
+            _PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER,
     };
     struct xc_dom_image_x86 *domx86 = dom->arch_private;
 
@@ -488,9 +488,8 @@ static int alloc_pgtables_x86_64(struct xc_dom_image *dom)
         .levels = PGTBL_LEVELS_X86_64,
         .vaddr_mask = bits_to_mask(VIRT_BITS_X86_64),
         .lvl_prot[0] = _PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED,
-        .lvl_prot[1] = 
_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER,
-        .lvl_prot[2] = 
_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER,
-        .lvl_prot[3] = 
_PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER,
+        .lvl_prot[1 ... 3] =
+            _PAGE_PRESENT|_PAGE_RW|_PAGE_ACCESSED|_PAGE_DIRTY|_PAGE_USER,
     };
     struct xc_dom_image_x86 *domx86 = dom->arch_private;
 
-- 
2.11.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel