Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> Huang Ying wrote:
>> On a system with CXL memory installed, the resource tree (/proc/iomem)
>> related to CXL memory looks like something as follows.
>>
>> 490000000-50fffffff : CXL Window 0
>> 490000000-50fffffff : region0
>> 490000000-50fffffff : dax0.0
>> 490000000-50fffffff : System RAM (kmem)
>>
>> When the following command line is run to try writing some memory in
>> CXL memory range,
>>
>> $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1
>> dd: error writing '/dev/mem': Bad address
>> 1+0 records in
>> 0+0 records out
>> 0 bytes copied, 0.0283507 s, 0.0 kB/s
>>
>> the command fails as expected. However, the error code is wrong. It
>> should be "Operation not permitted" instead of "Bad address". And,
>> the following warning is reported in kernel log.
>>
>> ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff
>> WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d
>> Modules linked in: cxl_pmem libnvdimm cbc encrypted_keys cxl_pmu
>> CPU: 2 UID: 0 PID: 416 Comm: dd Not tainted 6.11.0-rc3-kvm #40
>> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
>> RIP: 0010:__ioremap_caller.constprop.0+0x131/0x35d
>> Code: 2d 80 3d 24 6a a1 02 00 75 c1 48 8d 54 24 70 48 8d b4 24 90 00 00 00 48 c7 c7 40 3a 05 8a c6 05 07 6a a1 02 01 e8 a3 a0 01 00 <0f> 0b eb 9d 48 8b 84 24 90 00 00 00 48 8d 4c 24 60 89 ea 48 bf 00
>> RSP: 0018:ffff888105387bf0 EFLAGS: 00010282
>> RAX: 0000000000000000 RBX: 0000000490000fff RCX: 0000000000000000
>> RDX: 0000000000000001 RSI: 0000000000000003 RDI: ffffed1020a70f73
>> RBP: 0000000000000000 R08: ffffed100d9fce92 R09: 0000000000000001
>> R10: ffffffff892348e7 R11: ffffed100d9fce91 R12: 0000000490000000
>> R13: 0000000000000001 R14: 0000000000000001 R15: ffff888105387ca0
>> FS: 00007f86c438c740(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 000055ba75b1b818 CR3: 0000000005231000 CR4: 0000000000350eb0
>> Call Trace:
>> <TASK>
>> ? __warn+0xd7/0x1b8
>> ? __ioremap_caller.constprop.0+0x131/0x35d
>> ? report_bug+0x136/0x19e
>> ? __ioremap_caller.constprop.0+0x131/0x35d
>> ? handle_bug+0x3c/0x64
>> ? exc_invalid_op+0x13/0x38
>> ? asm_exc_invalid_op+0x16/0x20
>> ? irq_work_claim+0x16/0x38
>> ? __ioremap_caller.constprop.0+0x131/0x35d
>> ? tracer_hardirqs_off+0x18/0x16d
>> ? kmem_cache_debug_flags+0x16/0x23
>> ? memremap+0xcb/0x184
>> ? iounmap+0xfe/0xfe
>> ? lock_sync+0xc7/0xc7
>> ? lock_sync+0xc7/0xc7
>> ? rcu_is_watching+0x1c/0x38
>> ? do_raw_read_unlock+0x37/0x42
>> ? _raw_read_unlock+0x1f/0x2f
>> memremap+0xcb/0x184
>> ? pfn_valid+0x159/0x159
>> ? resource_is_exclusive+0xba/0xc5
>> xlate_dev_mem_ptr+0x25/0x2f
>> write_mem+0x94/0xfb
>> vfs_write+0x128/0x26d
>> ? kernel_write+0x89/0x89
>> ? rcu_is_watching+0x1c/0x38
>> ? __might_fault+0x72/0xba
>> ? __might_fault+0x72/0xba
>> ? rcu_is_watching+0x1c/0x38
>> ? lock_release+0xba/0x13e
>> ? files_lookup_fd_raw+0x40/0x4b
>> ? __fget_light+0x64/0x89
>> ksys_write+0xac/0xfe
>> ? __ia32_sys_read+0x40/0x40
>> ? tracer_hardirqs_off+0x18/0x16d
>> ? tracer_hardirqs_on+0x11/0x146
>> do_syscall_64+0x9a/0xfd
>> entry_SYSCALL_64_after_hwframe+0x4b/0x53
>> RIP: 0033:0x7f86c4487140
>> Code: 40 00 48 8b 15 c1 9c 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d a1 24 0e 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89
>> RSP: 002b:00007ffca9f62af8 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
>> RAX: ffffffffffffffda RBX: 0000000000000400 RCX: 00007f86c4487140
>> RDX: 0000000000000400 RSI: 000055ba75b1a000 RDI: 0000000000000001
>> RBP: 000055ba75b1a000 R08: 0000000000000000 R09: 00007f86c457c080
>> R10: 00007f86c43a84d0 R11: 0000000000000202 R12: 0000000000000000
>> R13: 0000000000000000 R14: 000055ba75b1a000 R15: 0000000000000400
>> </TASK>
>> irq event stamp: 0
>> hardirqs last enabled at (0): [<0000000000000000>] 0x0
>> hardirqs last disabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f
>> softirqs last enabled at (0): [<ffffffff89091e85>] copy_process+0xb60/0x255f
>> softirqs last disabled at (0): [<0000000000000000>] 0x0
>>
>> After investigation, we found the following bug.
>>
>> In the above resource tree, "System RAM" is a descendant of "CXL
>> Window 0" instead of a top level resource. So, region_intersects()
>> will report no System RAM resources in the CXL memory region
>> incorrectly, because it only checks the top level resources.
>> Consequently, devmem_is_allowed() will return 1 (allow access via
>> /dev/mem) for CXL memory region incorrectly. Fortunately, ioremap()
>> doesn't allow to map System RAM and reject the access.
>>
>> However, region_intersects() needs to be fixed to work correctly with
>> the resources tree with CXL Window as above. To fix it, we will
>> search matched resources in the descendant resources too. So, we will
>> not miss any matched resources anymore.
>
> Thanks for this Ying!
>
> I think this needs an explanation of the expected semantics of
> region_intersects() and maybe a fixup to meet that expectation, see
> below.
>
>> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
>> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
>> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
>> Cc: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
>> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
>> Cc: Alison Schofield <alison.schofield@xxxxxxxxx>
>> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
>> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
>> Cc: Alistair Popple <apopple@xxxxxxxxxx>
>> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> Cc: Baoquan He <bhe@xxxxxxxxxx>
>> ---
>> kernel/resource.c | 44 +++++++++++++++++++++++++++++++++++++-------
>> 1 file changed, 37 insertions(+), 7 deletions(-)
>>
>> diff --git a/kernel/resource.c b/kernel/resource.c
>> index 14777afb0a99..c97a5add9394 100644
>> --- a/kernel/resource.c
>> +++ b/kernel/resource.c
>> @@ -542,18 +542,48 @@ static int __region_intersects(struct resource *parent, resource_size_t start,
>> {
>> struct resource res;
>> int type = 0; int other = 0;
>> - struct resource *p;
>> + struct resource *p, *dp;
>> + resource_size_t ostart, oend;
>> + bool is_type;
>>
>> res.start = start;
>> res.end = start + size - 1;
>>
>> for (p = parent->child; p ; p = p->sibling) {
>> - bool is_type = (((p->flags & flags) == flags) &&
>> - ((desc == IORES_DESC_NONE) ||
>> - (desc == p->desc)));
>> -
>> - if (resource_overlaps(p, &res))
>> - is_type ? type++ : other++;
>> + if (!resource_overlaps(p, &res))
>> + continue;
>> + is_type = (((p->flags & flags) == flags) &&
>> + ((desc == IORES_DESC_NONE) || (desc == p->desc)));
>> + if (is_type) {
>> + type++;
>> + continue;
>> + }
>> + /*
>> + * Continue to search in descendant resources. Unless
>> + * the matched descendant resources cover the whole
>> + * overlapped range, increase 'other', because it
>> + * overlaps with 'p' at least.
>> + */
>> + other++;
>
> This results in REGION_MIXED whenever the target of the search is found
> as a descendant of @parent which I believe is unwanted.
This is not the behavior of this patch. There's a "other--" later in
this patch.
+ ostart = max(res.start, p->start);
+ oend = min(res.end, p->end);
+ for_each_resource(p, dp, false) {
+ if (!resource_overlaps(dp, &res))
+ continue;
+ is_type = (((dp->flags & flags) == flags) &&
+ ((desc == IORES_DESC_NONE) ||
+ (desc == dp->desc)));
+ if (is_type) {
+ type++;
+ if (dp->start > ostart)
+ break;
+ if (dp->end >= oend) {
+ other--; <====================== HERE!
+ break;
+ }
+ ostart = dp->end + 1;
+ }
+ }
}
if (type == 0)
That is, if the overlapped range is covered by matched (is_type == true)
descendant resources completely, other will not increase.
So, for resource tree as follows
490000000-52fffffff : CXL Window 0
490000000-50fffffff : region0
490000000-50fffffff : dax0.0
490000000-50fffffff : System RAM (kmem)
510000000-52fffffff
510000000-52fffffff : dax0.1
region_intersects(, 0x490000000, PAGE_SIZE, IORESOURCE_SYSTEM_RAM,
IORES_DESC_NONE) => REGION_INTERSECTS
region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM,
IORES_DESC_NONE) => REGION_MIXED
Even for
490000000-52fffffff : CXL Window 0
490000000-50fffffff : region0
490000000-50fffffff : dax0.0
490000000-50fffffff : System RAM (kmem)
region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM,
IORES_DESC_NONE) => REGION_MIXED
This isn't perfect, but it looks OK for me. Because for
490000000-50fffffff : System RAM
510000000-52fffffff : CXL Window 0
region_intersects(, 0x50f000000, 0x2000000, IORESOURCE_SYSTEM_RAM,
IORES_DESC_NONE) => REGION_MIXED
However, I admit that the original code is hard to be understood,
whether is something like below better?
for (p = parent->child; p ; p = p->sibling) {
if (!resource_overlaps(p, &res))
continue;
is_type = (((p->flags & flags) == flags) &&
((desc == IORES_DESC_NONE) || (desc == p->desc)));
if (is_type) {
type++;
continue;
}
/*
* Continue to search in descendant resources. Unless
* the matched descendant resources cover the whole
* overlapped range, increase 'other', because it
* overlaps with 'p' at least.
*/
covered = false;
ostart = max(res.start, p->start);
oend = min(res.end, p->end);
for_each_resource(p, dp, false) {
if (!resource_overlaps(dp, &res))
continue;
is_type = (((dp->flags & flags) == flags) &&
((desc == IORES_DESC_NONE) ||
(desc == dp->desc)));
if (is_type) {
type++;
if (dp->start > ostart)
break;
if (dp->end >= oend) {
covered = true;
break;
}
ostart = dp->end + 1;
}
}
if (!covered)
other++;
}
> The semantics of region_intersects() has always been within a single
> sibling level to date. So, I don't think @other should be incremented
> until @is_type is non-zero. It follows that if @is_type is set and
> !resource_contains(p, &res) then there is no point in descending because
> it is known at that there are no descendants to worry about.
Sorry, I don't understand your words here. Can you show your idea with
some examples or pseudo code?
> I do note that with those changes region_intersects() will start
> reporting REGION_MIXED rather than REGION_INTERSECTS when the passed in
> range intersects a hole plus the target, but I am not aware of any code
> path that expects to ignore resource holes. I.e. better to report holes
> as occupied in that case.
>
> Lastly, it would probably also be useful to special case the "@flags ==
> 0 && @desc == IORES_DESC_NONE" case because there is no point in
> descending the resource tree to look for additional holes. Those are all
> visible at the top of the resource tree.
--
Best Regards,
Huang, Ying
