On 2022-06-10 12:49 p.m., John David Anglin wrote:
>> The commit was added to prevent compiler optimisation from splitting
>> read/write operations.  I think it can lead in a change in opcodes but
>> must be safe.  So I'm not sure why the commit causes boot failure for now.
> Neither am I.
>>
>> I'm not familiar with PARISC and this may be a stupid question though,
>> what does `ldd` exactly do? and which line is it executed in the func/file?
> ldd performs a 64-bit load to register rp (r2).  It is part of mpt_reply's epilogue.
> The prior "sync" instruction corresponds to the "mb()" at the end of mpt_reply.
>
> I would have thought this code should have been write protected.  It seems
> CONFIG_STRICT_MODULE_RWX is not explicitly set in config:
>
> CONFIG_ARCH_HAS_STRICT_KERNEL_RWX=y
> CONFIG_STRICT_KERNEL_RWX=y
>
> I think I need to try enabling CONFIG_STRICT_MODULE_RWX.
With CONFIG_STRICT_MODULE_RWX, the fault went away and the system boots normally.

To enable CONFIG_STRICT_MODULE_RWX, I needed to add attached patch to Kconfig.

As far as I can tell, this only affects patch_map in the parisc backend:

static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags,
                                  int *need_unmap)
{
         unsigned long uintaddr = (uintptr_t) addr;
         bool module = !core_kernel_text(uintaddr);
         struct page *page;

         *need_unmap = 0;
         if (module && IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
                 page = vmalloc_to_page(addr);
         else if (!module && IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
                 page = virt_to_page(addr);
         else
                 return addr;

Possibly, this might affect Fusion MPT base driver but no patches are applied:

[   29.971295] mptbase alternatives: applied 0 out of 3 patches
[   29.971295] Fusion MPT base driver 3.04.20
[   29.971295] Copyright (c) 1999-2008 LSI Corporation
[   29.971295] Fusion MPT SPI Host driver 3.04.20

Dave

-- 
John David Anglin  dave.anglin@bell.net