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Message-ID: <50ECD89A.50100@oracle.com>
Date: Wed, 09 Jan 2013 10:40:26 +0800
From: ANNIE LI <annie.li@...cle.com>
To: Matt Wilson <msw@...zon.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Ian Campbell <Ian.Campbell@...rix.com>,
linux-kernel@...r.kernel.org, stable@...r.kernel.org,
xen-devel@...ts.xen.org
Subject: Re: [Xen-devel] [PATCH v2] xen/grant-table: correctly initialize
grant table version 1
Thanks so much for posting this.
On 2013-1-6 19:14, Matt Wilson wrote:
> Commit 85ff6acb075a484780b3d763fdf41596d8fc0970 (xen/granttable: Grant
> tables V2 implementation) changed the GREFS_PER_GRANT_FRAME macro from
> a constant to a conditional expression. The expression depends on
> grant_table_version being appropriately set. Unfortunately, at init
> time grant_table_version will be 0. The GREFS_PER_GRANT_FRAME
> conditional expression checks for "grant_table_version == 1", and
> therefore returns the number of grant references per frame for v2.
>
> This causes gnttab_init() to allocate fewer pages for gnttab_list, as
> a frame can old half the number of v2 entries than v1 entries. After
> gnttab_resume() is called, grant_table_version is appropriately
> set. nr_init_grefs will then be miscalculated and gnttab_free_count
> will hold a value larger than the actual number of free gref entries.
>
> If a guest is heavily utilizing improperly initialized v1 grant
> tables, memory corruption can occur. One common manifestation is
> corruption of the vmalloc list, resulting in a poisoned pointer
> derefrence when accessing /proc/meminfo or /proc/vmallocinfo:
>
> [ 40.770064] BUG: unable to handle kernel paging request at 0000200200001407
> [ 40.770083] IP: [<ffffffff811a6fb0>] get_vmalloc_info+0x70/0x110
> [ 40.770102] PGD 0
> [ 40.770107] Oops: 0000 [#1] SMP
> [ 40.770114] CPU 10
>
> This patch introduces a static variable, grefs_per_grant_frame, to
> cache the calculated value. gnttab_init() now calls
> gnttab_request_version() early so that grant_table_version and
> grefs_per_grant_frame can be appropriately set. A few BUG_ON()s have
> been added to prevent this type of bug from reoccurring in the future.
>
> Signed-off-by: Matt Wilson<msw@...zon.com>
> Reviewed-and-Tested-by: Steven Noonan<snoonan@...zon.com>
> Cc: Ian Campbell<Ian.Campbell@...rix.com>
> Cc: Konrad Rzeszutek Wilk<konrad.wilk@...cle.com>
> Cc: Annie Li<annie.li@...cle.com>
> Cc: xen-devel@...ts.xen.org
> Cc: linux-kernel@...r.kernel.org
> Cc: stable@...r.kernel.org # v3.3 and newer
> ---
> Changes since v1:
> * introduced a new gnttab_setup() function and moved all of the
> initialization code from gnttab_resume() there.
> ---
> drivers/xen/grant-table.c | 52 ++++++++++++++++++++++++++------------------
> 1 files changed, 31 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 043bf07..53715de 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -55,10 +55,6 @@
> /* External tools reserve first few grant table entries. */
> #define NR_RESERVED_ENTRIES 8
> #define GNTTAB_LIST_END 0xffffffff
> -#define GREFS_PER_GRANT_FRAME \
> -(grant_table_version == 1 ? \
> -(PAGE_SIZE / sizeof(struct grant_entry_v1)) : \
> -(PAGE_SIZE / sizeof(union grant_entry_v2)))
>
> static grant_ref_t **gnttab_list;
> static unsigned int nr_grant_frames;
> @@ -153,6 +149,7 @@ static struct gnttab_ops *gnttab_interface;
> static grant_status_t *grstatus;
>
> static int grant_table_version;
> +static int grefs_per_grant_frame;
>
> static struct gnttab_free_callback *gnttab_free_callback_list;
>
> @@ -766,12 +763,14 @@ static int grow_gnttab_list(unsigned int more_frames)
> unsigned int new_nr_grant_frames, extra_entries, i;
> unsigned int nr_glist_frames, new_nr_glist_frames;
>
> + BUG_ON(grefs_per_grant_frame == 0);
> +
> new_nr_grant_frames = nr_grant_frames + more_frames;
> - extra_entries = more_frames * GREFS_PER_GRANT_FRAME;
> + extra_entries = more_frames * grefs_per_grant_frame;
>
> - nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
> + nr_glist_frames = (nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;
> new_nr_glist_frames =
> - (new_nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
> + (new_nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;
> for (i = nr_glist_frames; i< new_nr_glist_frames; i++) {
> gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_ATOMIC);
> if (!gnttab_list[i])
> @@ -779,12 +778,12 @@ static int grow_gnttab_list(unsigned int more_frames)
> }
>
>
> - for (i = GREFS_PER_GRANT_FRAME * nr_grant_frames;
> - i< GREFS_PER_GRANT_FRAME * new_nr_grant_frames - 1; i++)
> + for (i = grefs_per_grant_frame * nr_grant_frames;
> + i< grefs_per_grant_frame * new_nr_grant_frames - 1; i++)
> gnttab_entry(i) = i + 1;
>
> gnttab_entry(i) = gnttab_free_head;
> - gnttab_free_head = GREFS_PER_GRANT_FRAME * nr_grant_frames;
> + gnttab_free_head = grefs_per_grant_frame * nr_grant_frames;
> gnttab_free_count += extra_entries;
>
> nr_grant_frames = new_nr_grant_frames;
> @@ -904,7 +903,8 @@ EXPORT_SYMBOL_GPL(gnttab_unmap_refs);
>
> static unsigned nr_status_frames(unsigned nr_grant_frames)
> {
> - return (nr_grant_frames * GREFS_PER_GRANT_FRAME + SPP - 1) / SPP;
> + BUG_ON(grefs_per_grant_frame == 0);
> + return (nr_grant_frames * grefs_per_grant_frame + SPP - 1) / SPP;
> }
>
> static int gnttab_map_frames_v1(xen_pfn_t *frames, unsigned int nr_gframes)
> @@ -1068,6 +1068,7 @@ static void gnttab_request_version(void)
> rc = HYPERVISOR_grant_table_op(GNTTABOP_set_version,&gsv, 1);
> if (rc == 0&& gsv.version == 2) {
> grant_table_version = 2;
> + grefs_per_grant_frame = PAGE_SIZE / sizeof(union grant_entry_v2);
> gnttab_interface =&gnttab_v2_ops;
> } else if (grant_table_version == 2) {
> /*
> @@ -1080,18 +1081,18 @@ static void gnttab_request_version(void)
> panic("we need grant tables version 2, but only version 1 is available");
> } else {
> grant_table_version = 1;
> + grefs_per_grant_frame = PAGE_SIZE / sizeof(struct grant_entry_v1);
> gnttab_interface =&gnttab_v1_ops;
> }
> - printk(KERN_INFO "Grant tables using version %d layout.\n",
> - grant_table_version);
> }
>
Is it better to keep printk here? In your last patch, you removed it
because gnttab_request_version and gnttab_resume are all called in
gnttab_init. and gnttab_resume also contains calling of
gnttab_request_version. But in this patch, gnttab_setup is used, and
does not have this issue now.
> -int gnttab_resume(void)
> +static int gnttab_setup(void)
> {
> unsigned int max_nr_gframes;
> char *kmsg = "Failed to kmalloc pages for pv in hvm grant frames\n";
>
> - gnttab_request_version();
> + printk(KERN_INFO "Grant tables using version %d layout.\n",
> + grant_table_version);
See comments above.
Thanks
Annie
> max_nr_gframes = gnttab_max_grant_frames();
> if (max_nr_gframes< nr_grant_frames)
> return -ENOSYS;
> @@ -1126,6 +1127,12 @@ int gnttab_resume(void)
> return 0;
> }
>
> +int gnttab_resume(void)
> +{
> + gnttab_request_version();
> + return gnttab_setup();
> +}
> +
> int gnttab_suspend(void)
> {
> gnttab_interface->unmap_frames();
> @@ -1137,9 +1144,10 @@ static int gnttab_expand(unsigned int req_entries)
> int rc;
> unsigned int cur, extra;
>
> + BUG_ON(grefs_per_grant_frame == 0);
> cur = nr_grant_frames;
> - extra = ((req_entries + (GREFS_PER_GRANT_FRAME-1)) /
> - GREFS_PER_GRANT_FRAME);
> + extra = ((req_entries + (grefs_per_grant_frame-1)) /
> + grefs_per_grant_frame);
> if (cur + extra> gnttab_max_grant_frames())
> return -ENOSPC;
>
> @@ -1157,21 +1165,23 @@ int gnttab_init(void)
> unsigned int nr_init_grefs;
> int ret;
>
> + gnttab_request_version();
> nr_grant_frames = 1;
> boot_max_nr_grant_frames = __max_nr_grant_frames();
>
> /* Determine the maximum number of frames required for the
> * grant reference free list on the current hypervisor.
> */
> + BUG_ON(grefs_per_grant_frame == 0);
> max_nr_glist_frames = (boot_max_nr_grant_frames *
> - GREFS_PER_GRANT_FRAME / RPP);
> + grefs_per_grant_frame / RPP);
>
> gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
> GFP_KERNEL);
> if (gnttab_list == NULL)
> return -ENOMEM;
>
> - nr_glist_frames = (nr_grant_frames * GREFS_PER_GRANT_FRAME + RPP - 1) / RPP;
> + nr_glist_frames = (nr_grant_frames * grefs_per_grant_frame + RPP - 1) / RPP;
> for (i = 0; i< nr_glist_frames; i++) {
> gnttab_list[i] = (grant_ref_t *)__get_free_page(GFP_KERNEL);
> if (gnttab_list[i] == NULL) {
> @@ -1180,12 +1190,12 @@ int gnttab_init(void)
> }
> }
>
> - if (gnttab_resume()< 0) {
> + if (gnttab_setup()< 0) {
> ret = -ENODEV;
> goto ini_nomem;
> }
>
> - nr_init_grefs = nr_grant_frames * GREFS_PER_GRANT_FRAME;
> + nr_init_grefs = nr_grant_frames * grefs_per_grant_frame;
>
> for (i = NR_RESERVED_ENTRIES; i< nr_init_grefs - 1; i++)
> gnttab_entry(i) = i + 1;
--
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