On Thu, 17 Nov 2022 at 20:04, Dave Hansen dave.hansen@intel.com wrote:
On 11/17/22 05:58, Marco Elver wrote:
[ 0.663761] WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/kfence.h:46 kfence_protect+0x7b/0x120 [ 0.664033] WARNING: CPU: 0 PID: 0 at mm/kfence/core.c:234 kfence_protect+0x7d/0x120 [ 0.664465] kfence: kfence_init failed
Any chance you could add some debugging and figure out what actually made kfence call over? Was it the pte or the level?
if (WARN_ON(!pte || level != PG_LEVEL_4K)) return false;I can see how the thing you bisected to might lead to a page table not being split, which could mess with the 'level' check.
Also, is there a reason this code is mucking with the page tables directly? It seems, uh, rather wonky. This, for instance:
if (protect) set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT)); else set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT)); /* * Flush this CPU's TLB, assuming whoever did the allocation/free is * likely to continue running on this CPU. */ preempt_disable(); flush_tlb_one_kernel(addr); preempt_enable();Seems rather broken. I assume the preempt_disable() is there to get rid of some warnings. But, there is nothing I can see to *keep* the CPU that did the free from being different from the one where the TLB flush is performed until the preempt_disable(). That makes the flush_tlb_one_kernel() mostly useless.
Is there a reason this code isn't using the existing page table manipulation functions and tries to code its own? What prevents it from using something like the attached patch?
I have applied this patch and found build warnings / errors.
In file included from mm/kfence/core.c:34: arch/x86/include/asm/kfence.h: In function 'kfence_protect_page': arch/x86/include/asm/kfence.h:45:17: error: implicit declaration of function 'set_memory_p'; did you mean 'set_memory_np'? [-Werror=implicit-function-declaration] 45 | set_memory_p(addr, addr + PAGE_SIZE); | ^~~~~~~~~~~~ | set_memory_np cc1: all warnings being treated as errors make[4]: *** [scripts/Makefile.build:250: mm/kfence/core.o] Error 1 In file included from mm/kfence/report.c:20: arch/x86/include/asm/kfence.h: In function 'kfence_protect_page': arch/x86/include/asm/kfence.h:45:17: error: implicit declaration of function 'set_memory_p'; did you mean 'set_memory_np'? [-Werror=implicit-function-declaration] 45 | set_memory_p(addr, addr + PAGE_SIZE); | ^~~~~~~~~~~~ | set_memory_np cc1: all warnings being treated as errors make[4]: *** [scripts/Makefile.build:250: mm/kfence/report.o] Error 1 In file included from mm/kfence/kfence_test.c:26: arch/x86/include/asm/kfence.h: In function 'kfence_protect_page': arch/x86/include/asm/kfence.h:45:17: error: implicit declaration of function 'set_memory_p'; did you mean 'set_memory_np'? [-Werror=implicit-function-declaration] 45 | set_memory_p(addr, addr + PAGE_SIZE); | ^~~~~~~~~~~~ | set_memory_np cc1: all warnings being treated as errors make[4]: *** [scripts/Makefile.build:250: mm/kfence/kfence_test.o] Error 1
ref: https://builds.tuxbuild.com/2HqMWcweeInju7rqVgGdNge7gby/
- Naresh