Re: [PATCH] xen/p2m: fix extra memory regions accounting

From: Juergen Gross
Date: Thu Sep 03 2015 - 08:25:49 EST

On 09/03/2015 02:05 PM, Roger Pau Monne wrote:
On systems with memory maps with ranges that don't end at page boundaries,

(XEN) 0000000000100000 - 00000000dfdf9c00 (usable)
(XEN) 00000000dfdf9c00 - 00000000dfe4bc00 (ACPI NVS)

xen_add_extra_mem will create a protected range that ends up at 0xdfdf9c00,
but the function used to check if a memory address is inside of a protected
range works with pfns, which means that an attempt to map 0xdfdf9c00 will be
refused because the check is performed against 0xdfdf9000 instead of

In order to fix this, make sure that the ranges that are added to the
xen_extra_mem array are aligned to page boundaries.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
AFAICT this patch needs to be backported to 3.19, 4.0, 4.1 and 4.2.
arch/x86/xen/setup.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 55f388e..dcf5865 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -68,6 +68,9 @@ static void __init xen_add_extra_mem(phys_addr_t start, phys_addr_t size)
int i;

+ start = PAGE_ALIGN(start);
+ size &= PAGE_MASK;

This is not correct. If start wasn't page aligned and size was, you'll
add one additional page to xen_extra_mem.

for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
/* Add new region. */
if (xen_extra_mem[i].size == 0) {
@@ -92,6 +95,9 @@ static void __init xen_del_extra_mem(phys_addr_t start, phys_addr_t size)
int i;
phys_addr_t start_r, size_r;

+ start = PAGE_ALIGN(start);
+ size &= PAGE_MASK;

Not really needed, as xen_del_extra_mem() is called with aligned values
only. OTOH it does no harm, as long as you correct size as above.

for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
start_r = xen_extra_mem[i].start;
size_r = xen_extra_mem[i].size;

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