Messages in this thread Patch in this message | | | Date | Mon, 7 Nov 2022 17:02:13 +0100 | From | Peter Zijlstra <> | Subject | Re: [tip:x86/mm] [x86/mm] b389949485: WARNING:at_arch/x86/mm/pat/set_memory.c:#__change_page_attr |
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On Mon, Nov 07, 2022 at 04:12:20PM +0100, Peter Zijlstra wrote: > On Sun, Nov 06, 2022 at 08:38:27PM +0800, kernel test robot wrote: > > > > Greeting, > > > > FYI, we noticed WARNING:at_arch/x86/mm/pat/set_memory.c:#__change_page_attr due to commit (built with gcc-11): > > > > commit: b38994948567e6d6b62947401c57f4ab2efe070c ("x86/mm: Implement native set_memory_rox()") > > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git x86/mm > > > > [test failed on linux-next/master 0cdb3579f1ee4c1e55acf8dfb0697b660067b1f8] > > > > in testcase: boot > > > > on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G > > > > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace): > > > > > > If you fix the issue, kindly add following tag > > | Reported-by: kernel test robot <oliver.sang@intel.com> > > | Link: https://lore.kernel.org/oe-lkp/202211061748.eb591682-oliver.sang@intel.com > > > > > > [ 44.943065][ T11] ------------[ cut here ]------------ > > [ 44.943725][ T11] CPA detected W^X violation: 0000000000000060 -> 0000000000000063 range: 0xffff8881beca5000 - 0xffff8881beca5fff PFN 1beca5 > > [ 44.944929][ T11] WARNING: CPU: 0 PID: 11 at arch/x86/mm/pat/set_memory.c:609 __change_page_attr (arch/x86/mm/pat/set_memory.c:609 arch/x86/mm/pat/set_memory.c:1582) > > [ 44.945824][ T11] Modules linked in: > > [ 44.946229][ T11] CPU: 0 PID: 11 Comm: kworker/0:1 Tainted: G W 6.1.0-rc3-00010-gb38994948567 #1 f37474c2082f37dd433f70907b94c2b0df8d70b8 > > [ 44.947518][ T11] Workqueue: events bpf_prog_free_deferred > > [ 44.948074][ T11] RIP: 0010:__change_page_attr (arch/x86/mm/pat/set_memory.c:609 arch/x86/mm/pat/set_memory.c:1582) > > Urgh, as spotted by dhansen, the code in change_page_attr_set_clr(), > specifically the checkalias thing, seems to rely on single bit flips for > NX. > > Let me try to make sense of this stuff....
This appears to appease the test case, but I definitely need to look at this again with a fresh mind, horrid stuff this and I'm sure I hate this patch.
--- diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index f275605892df..07339ac8bc41 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -69,10 +69,11 @@ static const int cpa_warn_level = CPA_PROTECT; */ static DEFINE_SPINLOCK(cpa_lock); -#define CPA_FLUSHTLB 1 -#define CPA_ARRAY 2 -#define CPA_PAGES_ARRAY 4 -#define CPA_NO_CHECK_ALIAS 8 /* Do not search for aliases */ +#define CPA_FLUSHTLB 0x01 +#define CPA_ARRAY 0x02 +#define CPA_PAGES_ARRAY 0x04 +#define CPA_NO_CHECK_ALIAS 0x08 /* Do not search for aliases */ +#define CPA_HAS_NX 0x10 static inline pgprot_t cachemode2pgprot(enum page_cache_mode pcm) { @@ -1708,9 +1709,21 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias) goto out; if (checkalias) { - ret = cpa_process_alias(cpa); - if (ret) - goto out; + pgprot_t set = cpa->mask_set; + pgprot_t clr = cpa->mask_clr; + + if (cpa->flags & CPA_HAS_NX) { + cpa->mask_set.pgprot &= ~_PAGE_NX; + cpa->mask_clr.pgprot &= ~_PAGE_NX; + } + if (pgprot_val(cpa->mask_set) | pgprot_val(cpa->mask_clr)) { + ret = cpa_process_alias(cpa); + if (ret) + goto out; + } + + cpa->mask_set = set; + cpa->mask_clr = clr; } /* @@ -1788,8 +1801,10 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages, if (in_flag & (CPA_ARRAY | CPA_PAGES_ARRAY)) cpa.flags |= in_flag; - /* No alias checking for _NX bit modifications */ - checkalias = (pgprot_val(mask_set) | pgprot_val(mask_clr)) != _PAGE_NX; + if ((pgprot_val(mask_set) | pgprot_val(mask_clr)) & _PAGE_NX) + cpa.flags |= CPA_HAS_NX; + + checkalias = 1; /* Has caller explicitly disabled alias checking? */ if (in_flag & CPA_NO_CHECK_ALIAS) checkalias = 0;
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