Re: [PATCH v5 0/6] Move swapper_pg_dir to rodata section.

[James Morse]

Hi Catalin, Mark,

On 25/09/18 15:06, Mark Rutland wrote:
> On Tue, Sep 25, 2018 at 05:53:16PM +0800, Jun Yao wrote:
>> On Mon, Sep 24, 2018 at 06:19:36PM +0100, Mark Rutland wrote:
>>> I've pushed a branch with the cleanups I requested [1] folded in.
>>>
>>> I'm still a bit worried about the pgd lock, but otherwise I think this
>>> is sound. I intend to throw some testing at it, just in case.
>>>
>>> If you're happy with that branch, I'll ask Will and Catalin to consider
>>> picking it up.
>>
>> This branch looks great. Thank you for improving my patch.
> 
> Thanks for your patches!
> 
>> Is there anything I need to do? This is my first time to submit a patch,
>> so I am a bit overwhelmed. I think I should wait for other people to
>> review my patch. If there is a problem, I need to fix it.
> 
> Hopefully Catalin is happy to pick this up from my branch, and neither
> of us have to do anything. :)
> 
> Catalin, are you happy to pick the patches from:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/ro-swapper
> 
> ... that should be based on the arm64 for-next/core branch, and has
> James's R-B prior to my commit fixup notes.
> 
> I've given this some basic testing with defconfig, 48-bit/4k and
> 42-bit/64k (with lockdep on in both cases), and things seem fine.

Re-running my hacky tests for this series knocks for-next/core over:
| Unable to handle kernel write to read-only memory at virtual address
fffffc00092b0008
| Mem abort info:
|   ESR = 0x9600004f
|   Exception class = DABT (current EL), IL = 32 bits
|   SET = 0, FnV = 0
|   EA = 0, S1PTW = 0
| Data abort info:
|   ISV = 0, ISS = 0x0000004f
|   CM = 0, WnR = 1
| swapper pgtable: 64k pages, 42-bit VAs, pgdp = 00000000992f9c42
| [fffffc00092b0008] pgd=00000087ffff0803, pud=00000087ffff0803,
pmd=00000087ffff0803, pte=00e00080032b0f93
| Internal error: Oops: 9600004f [#1] PREEMPT SMP
| Modules linked in:
| CPU: 4 PID: 13938 Comm: hackbench Tainted: G        W
4.19.0-rc2-00063-gc219bc4e9205 #10628
| Hardware name: AMD Seattle (Rev.B0) Development Board (Overdrive) (DT)
| pstate: a0400005 (NzCv daif +PAN -UAO)
| pc : __pte_alloc_kernel+0x60/0xd8
| lr : __pte_alloc_kernel+0x44/0xd8

| Process hackbench (pid: 13938, stack limit = 0x000000007ca756ec)
| Call trace:
|  __pte_alloc_kernel+0x60/0xd8
|  vmap_page_range_noflush+0x1bc/0x1d8
|  map_vm_area+0x30/0x40
|  __vmalloc_node_range+0x1e4/0x2e8
|  copy_process.isra.3.part.4+0x1e8/0x1ae8
|  _do_fork+0xd0/0x7f0
|  __arm64_sys_clone+0x1c/0x28

|  el0_svc_handler+0x7c/0x130

|  el0_svc+0x8/0xc

| Code: 90007b60 f946e000 cb000273 b2400673 (f9000293)

|  ---[ end trace 7bf2d2ffce498c7a ]---

| Kernel panic - not syncing: Fatal exception


The below patch fixes it: I'll post it properly shortly...
-----------------------%<-----------------------
Author: James Morse <james.morse@xxxxxxx>
Date:   Wed Oct 3 12:03:38 2018 +0100

    asm-generic/pgtable-nop?d.h: define folded with a value for use in C

    It turns out "if (__is_defined(__PAGETABLE_PMD_FOLDED))" isn't equivalent
    to "#ifdef __PAGETABLE_PMD_FOLDED". (who knew!)

    kconfig.h's __is_defined() expects a define of the form
    "#define CONFIG_BOOGER 1". But these nop?d headers just have
    "#define __PAGETABLE_PMD_FOLDED".

    This means ____is_defined()'s triplet passed to __take_second_arg() is
    'empty-string 1 0' in both cases, meaning these symbols can't be used
    from C. (they are always false).

    asm-generic gets away with this as its using the pre-processor's
    defined() macro on this, not the C __is_defined().

    Add the expected '1'.

    Signed-off-by: James Morse <james.morse@xxxxxxx>

diff --git a/include/asm-generic/pgtable-nopmd.h
b/include/asm-generic/pgtable-nopmd.h
index f35f6e8149e4..fcb4769a075a 100644
--- a/include/asm-generic/pgtable-nopmd.h
+++ b/include/asm-generic/pgtable-nopmd.h
@@ -8,7 +8,7 @@

 struct mm_struct;

-#define __PAGETABLE_PMD_FOLDED
+#define __PAGETABLE_PMD_FOLDED 1

 /*
  * Having the pmd type consist of a pud gets the size right, and allows
diff --git a/include/asm-generic/pgtable-nopud.h
b/include/asm-generic/pgtable-nopud.h
index e950b9c50f34..d300dbcddaf3 100644
--- a/include/asm-generic/pgtable-nopud.h
+++ b/include/asm-generic/pgtable-nopud.h
@@ -9,7 +9,7 @@
 #else
 #include <asm-generic/pgtable-nop4d.h>

-#define __PAGETABLE_PUD_FOLDED
+#define __PAGETABLE_PUD_FOLDED 1

 /*
  * Having the pud type consist of a p4d gets the size right, and allows
-----------------------%<-----------------------


(and, while digging through this, I spotted:
| #define set_pmd_at(mm, addr, pmdp, pmd)	
|	set_pte_at(mm, addr, (pte_t *)pmdp, pmd_pte(pmd))
which may trip up too)


Thanks,

James