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After use_asid_allocator is enabled, the userspace application will
crash by stale TLB entries. Because only using cpumask_clear_cpu without
local_flush_tlb_all couldn't guarantee CPU's TLB entries were fresh.
Then set_mm_asid would cause the user space application to get a stale
value by stale TLB entry, but set_mm_noasid is okay.
Here is the symptom of the bug:
unhandled signal 11 code 0x1 (coredump)
0x0000003fd6d22524 <+4>: auipc s0,0x70
0x0000003fd6d22528 <+8>: ld s0,-148(s0) # 0x3fd6d92490
=> 0x0000003fd6d2252c <+12>: ld a5,0(s0)
(gdb) i r s0
s0 0x8082ed1cc3198b21 0x8082ed1cc3198b21
(gdb) x /2x 0x3fd6d92490
0x3fd6d92490: 0xd80ac8a8 0x0000003f
The core dump file shows that register s0 is wrong, but the value in
memory is correct. Because 'ld s0, -148(s0)' used a stale mapping entry
in TLB and got a wrong result from an incorrect physical address.
When the task ran on CPU0, which loaded/speculative-loaded the value of
address(0x3fd6d92490), then the first version of the mapping entry was
PTWed into CPU0's TLB.
When the task switched from CPU0 to CPU1 (No local_tlb_flush_all here by
asid), it happened to write a value on the address (0x3fd6d92490). It
caused do_page_fault -> wp_page_copy -> ptep_clear_flush ->
ptep_get_and_clear & flush_tlb_page.
The flush_tlb_page used mm_cpumask(mm) to determine which CPUs need TLB
flush, but CPU0 had cleared the CPU0's mm_cpumask in the previous
switch_mm. So we only flushed the CPU1 TLB and set the second version
mapping of the PTE. When the task switched from CPU1 to CPU0 again, CPU0
still used a stale TLB mapping entry which contained a wrong target
physical address. It raised a bug when the task happened to read that
value.
CPU0 CPU1
- switch 'task' in
- read addr (Fill stale mapping
entry into TLB)
- switch 'task' out (no tlb_flush)
- switch 'task' in (no tlb_flush)
- write addr cause pagefault
do_page_fault() (change to
new addr mapping)
wp_page_copy()
ptep_clear_flush()
ptep_get_and_clear()
& flush_tlb_page()
write new value into addr
- switch 'task' out (no tlb_flush)
- switch 'task' in (no tlb_flush)
- read addr again (Use stale
mapping entry in TLB)
get wrong value from old phyical
addr, BUG!
The solution is to keep all CPUs' footmarks of cpumask(mm) in switch_mm,
which could guarantee to invalidate all stale TLB entries during TLB
flush.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.