On Mon, Aug 19, 2024 at 10:34:13AM +0800, 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 Submitting Patches documentation suggests how to shrink the above to make it somewhat readable and important. > 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, if we found a > unmatched resource in the top level, we will continue to search > matched resources in its descendant resources. So, we will not miss > any matched resources in resource tree anymore. In the new > implementation, > > |------------- "CXL Window 0" ------------| > |-- "System RAM" --| > > will look as if > > |-- "System RAM" --||-- "CXL Window 0a" --| > > in effect. > Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > 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> You may move Cc list after '---', so it won't unnecessarily pollute the commit message. > --- > Changelogs: > > v2: > > - Fix a bug which occurs when descendant of a matched resource matches. > > - Revise the patch description and comments to make the algorithm clearer. > Thanks Dan and David's comments! > > - Link to v1: https://lore.kernel.org/linux-mm/20240816020723.771196-1-ying.huang@xxxxxxxxx/ ... > { > struct resource res; > int type = 0; int other = 0; > - struct resource *p; > + struct resource *p, *dp; > + resource_size_t ostart, oend; > + bool is_type, covered; Maybe keep more reversed xmas tree ordering? > 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))); In the original code and here the most outer parentheses are redundant. > + if (is_type) { > + type++; > + continue; > + } > + /* > + * Continue to search in descendant resources as if the > + * matched descendant resources cover some ranges of 'p'. > + * > + * |------------- "CXL Window 0" ------------| > + * |-- "System RAM" --| > + * > + * looks as if > + * > + * |-- "System RAM" --||-- "CXL Window 0a" --| > + * > + * in effect. > + */ > + covered = false; > + ostart = max(res.start, p->start); > + oend = min(res.end, p->end); Isn't a reinvention of resource_intersection()? With that in place you may also drop the above resource_overlaps(). > + 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))); Most outer parentheses are redundant. With them being dropped you also may unite the last two lines into a single one. > + if (is_type) { > + type++; > + if (dp->start > ostart) > + break; > + if (dp->end >= oend) { > + covered = true; > + break; > + } > + ostart = max(ostart, dp->end + 1); > + } > + } > + if (!covered) > + other++; > } -- With Best Regards, Andy Shevchenko
