[PATCH] MIPS: fix pmd_mkinvalid

[PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
return true.
So introduce a _PAGE_PRESENT_INVALID_SHIFT bit to check if a pmd is
present but invalidated by pmd_mkinvalid.

Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
---
 arch/mips/include/asm/pgtable-64.h   | 2 +-
 arch/mips/include/asm/pgtable-bits.h | 5 +++++
 arch/mips/include/asm/pgtable.h      | 3 ++-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
index 41921ac..1c5ef41 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -265,7 +265,7 @@ static inline int pmd_present(pmd_t pmd)
 {
 #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 	if (unlikely(pmd_val(pmd) & _PAGE_HUGE))
-		return pmd_val(pmd) & _PAGE_PRESENT;
+		return pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PRESENT_INVALID);
 #endif
 
 	return pmd_val(pmd) != (unsigned long) invalid_pte_table;
diff --git a/arch/mips/include/asm/pgtable-bits.h b/arch/mips/include/asm/pgtable-bits.h
index 2362842..3c176a1e 100644
--- a/arch/mips/include/asm/pgtable-bits.h
+++ b/arch/mips/include/asm/pgtable-bits.h
@@ -49,6 +49,7 @@ enum pgtable_bits {
 
 	/* Used only by software (masked out before writing EntryLo*) */
 	_PAGE_PRESENT_SHIFT = 24,
+	_PAGE_PRESENT_INVALID_SHIFT,
 	_PAGE_WRITE_SHIFT,
 	_PAGE_ACCESSED_SHIFT,
 	_PAGE_MODIFIED_SHIFT,
@@ -80,6 +81,7 @@ enum pgtable_bits {
 
 	/* Used only by software (masked out before writing EntryLo*) */
 	_PAGE_PRESENT_SHIFT = _CACHE_SHIFT + 3,
+	_PAGE_PRESENT_INVALID_SHIFT,
 	_PAGE_NO_READ_SHIFT,
 	_PAGE_WRITE_SHIFT,
 	_PAGE_ACCESSED_SHIFT,
@@ -98,6 +100,7 @@ enum pgtable_bits {
 enum pgtable_bits {
 	/* Used only by software (writes to EntryLo ignored) */
 	_PAGE_PRESENT_SHIFT,
+	_PAGE_PRESENT_INVALID_SHIFT,
 	_PAGE_NO_READ_SHIFT,
 	_PAGE_WRITE_SHIFT,
 	_PAGE_ACCESSED_SHIFT,
@@ -122,6 +125,7 @@ enum pgtable_bits {
 enum pgtable_bits {
 	/* Used only by software (masked out before writing EntryLo*) */
 	_PAGE_PRESENT_SHIFT,
+	_PAGE_PRESENT_INVALID_SHIFT,
 #if !defined(CONFIG_CPU_HAS_RIXI)
 	_PAGE_NO_READ_SHIFT,
 #endif
@@ -152,6 +156,7 @@ enum pgtable_bits {
 
 /* Used only by software */
 #define _PAGE_PRESENT		(1 << _PAGE_PRESENT_SHIFT)
+#define _PAGE_PRESENT_INVALID	(1 << _PAGE_PRESENT_INVALID_SHIFT)
 #define _PAGE_WRITE		(1 << _PAGE_WRITE_SHIFT)
 #define _PAGE_ACCESSED		(1 << _PAGE_ACCESSED_SHIFT)
 #define _PAGE_MODIFIED		(1 << _PAGE_MODIFIED_SHIFT)
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 374c632..cc80211 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -698,7 +698,8 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 
 static inline pmd_t pmd_mkinvalid(pmd_t pmd)
 {
-	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
+	pmd_val(pmd) |= _PAGE_PRESENT_INVALID;
+	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID);
 
 	return pmd;
 }
-- 
1.8.3.1

Re: [PATCH] MIPS: fix pmd_mkinvalid

[kernel test robot]

Hi Hongchen,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.19-rc5 next-20220706]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Hongchen-Zhang/MIPS-fix-pmd_mkinvalid/20220706-171327
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git e35e5b6f695d241ffb1d223207da58a1fbcdff4b
config: mips-maltaaprp_defconfig (https://download.01.org/0day-ci/archive/20220707/202207070340.HGbiEUlO-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project f553287b588916de09c66e3e32bf75e5060f967f)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install mips cross compiling tool for clang build
        # apt-get install binutils-mipsel-linux-gnu
        # https://github.com/intel-lab-lkp/linux/commit/cc17741b8218515ea05dd64f5db2402a67e7a821
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Hongchen-Zhang/MIPS-fix-pmd_mkinvalid/20220706-171327
        git checkout cc17741b8218515ea05dd64f5db2402a67e7a821
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   arch/mips/mm/init.c:60:6: warning: no previous prototype for function 'setup_zero_pages' [-Wmissing-prototypes]
   void setup_zero_pages(void)
        ^
   arch/mips/mm/init.c:60:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void setup_zero_pages(void)
   ^
   static 
>> arch/mips/mm/init.c:454:2: error: call to __compiletime_assert_347 declared with 'error' attribute: BUILD_BUG_ON failed: IS_ENABLED(CONFIG_32BIT) && (_PFN_SHIFT > PAGE_SHIFT)
           BUILD_BUG_ON(IS_ENABLED(CONFIG_32BIT) && (_PFN_SHIFT > PAGE_SHIFT));
           ^
   include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
           BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
           ^
   include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
   #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                       ^
   include/linux/compiler_types.h:354:2: note: expanded from macro 'compiletime_assert'
           _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
           ^
   include/linux/compiler_types.h:342:2: note: expanded from macro '_compiletime_assert'
           __compiletime_assert(condition, msg, prefix, suffix)
           ^
   include/linux/compiler_types.h:335:4: note: expanded from macro '__compiletime_assert'
                           prefix ## suffix();                             \
                           ^
   <scratch space>:174:1: note: expanded from here
   __compiletime_assert_347
   ^
   1 warning and 1 error generated.


vim +/error +454 arch/mips/mm/init.c

1132137e87898d Jiang Liu   2013-07-03  447  
1132137e87898d Jiang Liu   2013-07-03  448  void __init mem_init(void)
1132137e87898d Jiang Liu   2013-07-03  449  {
05d013a0366d50 Paul Burton 2019-09-18  450  	/*
05d013a0366d50 Paul Burton 2019-09-18  451  	 * When _PFN_SHIFT is greater than PAGE_SHIFT we won't have enough PTE
05d013a0366d50 Paul Burton 2019-09-18  452  	 * bits to hold a full 32b physical address on MIPS32 systems.
05d013a0366d50 Paul Burton 2019-09-18  453  	 */
05d013a0366d50 Paul Burton 2019-09-18 @454  	BUILD_BUG_ON(IS_ENABLED(CONFIG_32BIT) && (_PFN_SHIFT > PAGE_SHIFT));
05d013a0366d50 Paul Burton 2019-09-18  455  

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

[PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
return true.
So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
present but invalidated by pmd_mkinvalid.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
---
 arch/mips/include/asm/pgtable-64.h   | 2 +-
 arch/mips/include/asm/pgtable-bits.h | 2 ++
 arch/mips/include/asm/pgtable.h      | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
index 41921ac..050cf66 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -265,7 +265,7 @@ static inline int pmd_present(pmd_t pmd)
 {
 #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 	if (unlikely(pmd_val(pmd) & _PAGE_HUGE))
-		return pmd_val(pmd) & _PAGE_PRESENT;
+		return pmd_val(pmd) & (_PAGE_PRESENT | _PMD_PRESENT_INVALID);
 #endif
 
 	return pmd_val(pmd) != (unsigned long) invalid_pte_table;
diff --git a/arch/mips/include/asm/pgtable-bits.h b/arch/mips/include/asm/pgtable-bits.h
index 2362842..72cd88a 100644
--- a/arch/mips/include/asm/pgtable-bits.h
+++ b/arch/mips/include/asm/pgtable-bits.h
@@ -130,6 +130,7 @@ enum pgtable_bits {
 	_PAGE_MODIFIED_SHIFT,
 #if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
 	_PAGE_HUGE_SHIFT,
+	_PMD_PRESENT_INVALID_SHIFT,
 #endif
 #if defined(CONFIG_ARCH_HAS_PTE_SPECIAL)
 	_PAGE_SPECIAL_SHIFT,
@@ -157,6 +158,7 @@ enum pgtable_bits {
 #define _PAGE_MODIFIED		(1 << _PAGE_MODIFIED_SHIFT)
 #if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
 # define _PAGE_HUGE		(1 << _PAGE_HUGE_SHIFT)
+#define _PMD_PRESENT_INVALID	(1 << _PMD_PRESENT_INVALID_SHIFT)
 #endif
 #if defined(CONFIG_ARCH_HAS_PTE_SPECIAL)
 # define _PAGE_SPECIAL		(1 << _PAGE_SPECIAL_SHIFT)
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 374c632..a75f461 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -696,12 +696,15 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 	return pmd;
 }
 
+#ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 static inline pmd_t pmd_mkinvalid(pmd_t pmd)
 {
+	pmd_val(pmd) |= _PMD_PRESENT_INVALID;
 	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
 
 	return pmd;
 }
+#endif
 
 /*
  * The generic version pmdp_huge_get_and_clear uses a version of pmd_clear() with a
-- 
1.8.3.1

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Thomas Bogendoerfer]

On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
> When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
> return true.
> So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
> present but invalidated by pmd_mkinvalid.

What problem are you trying to fix ? What are the symptoms ?

> Reported-by: kernel test robot <lkp@intel.com>

the test robot showed problems with your last version of the patch,
which hasn't been integrated into at least the MIPS tree, so no
need to that.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

On 2022/7/7 下午5:22, Thomas Bogendoerfer wrote:
> On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
>> When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
>> return true.
>> So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
>> present but invalidated by pmd_mkinvalid.
> 
> What problem are you trying to fix ? What are the symptoms ?
> 
>> Reported-by: kernel test robot <lkp@intel.com>
> 
> the test robot showed problems with your last version of the patch,
> which hasn't been integrated into at least the MIPS tree, so no
> need to that.
> 
> Thomas.
> 

Hi Thomas,
   The idea come from the commit:
   b65399f6111b(arm64/mm: Change THP helpers to comply with generic MM 
  semantics).
   There is an problem now:
	    CPU 0		CPU 1
	pmdp_invalidate		do_page_fault		
	...			  __handle_mm_fault
				    is_swap_pmd == true
				    trigger VM_BUG_ON() ?
	set_pmd_at
   the reason is that pmd_present return true,after this commit
   pmd_present will return false,and the VM_BUG_ON will not be triggered.
   Like arm64 does,we can introduce a new bit to fix this.

Thanks.

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

On 2022/7/7 下午7:12, Hongchen Zhang wrote:
> On 2022/7/7 下午5:22, Thomas Bogendoerfer wrote:
>> On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
>>> When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
>>> return true.
>>> So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
>>> present but invalidated by pmd_mkinvalid.
>>
>> What problem are you trying to fix ? What are the symptoms ?
>>
>>> Reported-by: kernel test robot <lkp@intel.com>
>>
>> the test robot showed problems with your last version of the patch,
>> which hasn't been integrated into at least the MIPS tree, so no
>> need to that.
>>
>> Thomas.
>>
> 
> Hi Thomas,
>    The idea come from the commit:
>    b65399f6111b(arm64/mm: Change THP helpers to comply with generic MM 
>   semantics).
>    There is an problem now:
>          CPU 0        CPU 1
>      pmdp_invalidate        do_page_fault
>      ...              __handle_mm_fault
>                      is_swap_pmd == true
>                      trigger VM_BUG_ON() ?
>      set_pmd_at
>    the reason is that pmd_present return true,after this commit
>    pmd_present will return false,and the VM_BUG_ON will not be triggered.
>    Like arm64 does,we can introduce a new bit to fix this.
> 
> Thanks.
Hi Thomas,
  Is there problem of this patch? What's your opinion of this patch?

Thanks

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Thomas Bogendoerfer]

On Tue, Jul 12, 2022 at 06:01:08PM +0800, Hongchen Zhang wrote:
> On 2022/7/7 下午7:12, Hongchen Zhang wrote:
> > On 2022/7/7 下午5:22, Thomas Bogendoerfer wrote:
> > > On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
> > > > When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
> > > > return true.
> > > > So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
> > > > present but invalidated by pmd_mkinvalid.
> > > 
> > > What problem are you trying to fix ? What are the symptoms ?
> > > 
> > > > Reported-by: kernel test robot <lkp@intel.com>
> > > 
> > > the test robot showed problems with your last version of the patch,
> > > which hasn't been integrated into at least the MIPS tree, so no
> > > need to that.
> > > 
> > > Thomas.
> > > 
> > 
> > Hi Thomas,
> >    The idea come from the commit:
> >    b65399f6111b(arm64/mm: Change THP helpers to comply with generic MM
> >  semantics).
> >    There is an problem now:
> >          CPU 0        CPU 1
> >      pmdp_invalidate        do_page_fault
> >      ...              __handle_mm_fault
> >                      is_swap_pmd == true
> >                      trigger VM_BUG_ON() ?
> >      set_pmd_at
> >    the reason is that pmd_present return true,after this commit
> >    pmd_present will return false,and the VM_BUG_ON will not be triggered.
> >    Like arm64 does,we can introduce a new bit to fix this.
> > 
> > Thanks.
> Hi Thomas,
>  Is there problem of this patch? What's your opinion of this patch?

I haven't dig deeper into it, but needing more page bits is a pain
for 32bit kernel and would make it nearly impossible to get huge
page support there. And the description you gave me, needs to be
in the commit description.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

On 2022/7/12 下午7:19, Thomas Bogendoerfer wrote:
> On Tue, Jul 12, 2022 at 06:01:08PM +0800, Hongchen Zhang wrote:
>> On 2022/7/7 下午7:12, Hongchen Zhang wrote:
>>> On 2022/7/7 下午5:22, Thomas Bogendoerfer wrote:
>>>> On Thu, Jul 07, 2022 at 04:11:35PM +0800, Hongchen Zhang wrote:
>>>>> When a pmd entry is invalidated by pmd_mkinvalid,pmd_present should
>>>>> return true.
>>>>> So introduce a _PMD_PRESENT_INVALID_SHIFT bit to check if a pmd is
>>>>> present but invalidated by pmd_mkinvalid.
>>>>
>>>> What problem are you trying to fix ? What are the symptoms ?
>>>>
>>>>> Reported-by: kernel test robot <lkp@intel.com>
>>>>
>>>> the test robot showed problems with your last version of the patch,
>>>> which hasn't been integrated into at least the MIPS tree, so no
>>>> need to that.
>>>>
>>>> Thomas.
>>>>
>>>
>>> Hi Thomas,
>>>     The idea come from the commit:
>>>     b65399f6111b(arm64/mm: Change THP helpers to comply with generic MM
>>>   semantics).
>>>     There is an problem now:
>>>           CPU 0        CPU 1
>>>       pmdp_invalidate        do_page_fault
>>>       ...              __handle_mm_fault
>>>                       is_swap_pmd == true
>>>                       trigger VM_BUG_ON() ?
>>>       set_pmd_at
>>>     the reason is that pmd_present return true,after this commit
>>>     pmd_present will return false,and the VM_BUG_ON will not be triggered.
>>>     Like arm64 does,we can introduce a new bit to fix this.
>>>
>>> Thanks.
>> Hi Thomas,
>>   Is there problem of this patch? What's your opinion of this patch?
> 
> I haven't dig deeper into it, but needing more page bits is a pain
> for 32bit kernel and would make it nearly impossible to get huge
> page support there. And the description you gave me, needs to be
> in the commit description.
> 
> Thomas.
> 
Hi Thomas,
  Thanks for your patiently review. For your question,
   1. I think there may be problem when compile 32bit kernel with huge 
page support,because _PAGE_HUGE_SHIFT is only defined for R4K now.
   2. I will modify the commit as you said and make a v2 patch.

Thanks.
Hongchen Zhang

[PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

pmd_mkinvalid should not clear dirty flag,otherwise the pmd
dirty flag,it's ok to just clear _PAGE_VALID.

Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
---
 arch/mips/include/asm/pgtable.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 374c632..d30a186 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -698,7 +698,7 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
 
 static inline pmd_t pmd_mkinvalid(pmd_t pmd)
 {
-	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
+	pmd_val(pmd) &= ~_PAGE_VALID;
 
 	return pmd;
 }
-- 
1.8.3.1

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Jiaxun Yang]

在 2022/5/31 5:36, Hongchen Zhang 写道:
> pmd_mkinvalid should not clear dirty flag,otherwise the pmd
> dirty flag,it's ok to just clear _PAGE_VALID.
Hi Hongcheng,

Sorry, what is meant by "otherwise the pmd dirty flag"? Could you please
elaborate?
In my humble opinion _PAGE_PRESENT must be cleared in mkinvalid as it
nolonger present here. And thus it lose the dirty status.

Thanks
- Jiaxun

> Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
> ---
>   arch/mips/include/asm/pgtable.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
> index 374c632..d30a186 100644
> --- a/arch/mips/include/asm/pgtable.h
> +++ b/arch/mips/include/asm/pgtable.h
> @@ -698,7 +698,7 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
>   
>   static inline pmd_t pmd_mkinvalid(pmd_t pmd)
>   {
> -	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
> +	pmd_val(pmd) &= ~_PAGE_VALID;
>   
>   	return pmd;
>   }

Re: [PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

On 2022/5/31 下午11:40, Jiaxun Yang wrote:
> 
> 
> 在 2022/5/31 5:36, Hongchen Zhang 写道:
>> pmd_mkinvalid should not clear dirty flag,otherwise the pmd
>> dirty flag,it's ok to just clear _PAGE_VALID.
> Hi Hongcheng,
> 
> Sorry, what is meant by "otherwise the pmd dirty flag"? Could you please
> elaborate?
> In my humble opinion _PAGE_PRESENT must be cleared in mkinvalid as it
> nolonger present here. And thus it lose the dirty status.
> 
> Thanks
> - Jiaxun
> 
>> Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn>
>> ---
>>   arch/mips/include/asm/pgtable.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/mips/include/asm/pgtable.h 
>> b/arch/mips/include/asm/pgtable.h
>> index 374c632..d30a186 100644
>> --- a/arch/mips/include/asm/pgtable.h
>> +++ b/arch/mips/include/asm/pgtable.h
>> @@ -698,7 +698,7 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t 
>> newprot)
>>   static inline pmd_t pmd_mkinvalid(pmd_t pmd)
>>   {
>> -    pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY);
>> +    pmd_val(pmd) &= ~_PAGE_VALID;
>>       return pmd;
>>   }
Hi Jiaxun,

Refer to [ https://lkml.org/lkml/2018/10/17/231 ],Andrea said "
The clear of the real present bit during pmd (virtual) splitting is
done with pmdp_invalidate, that is created specifically to keeps
pmd_trans_huge=true, pmd_present=true despite the present bit is not
set. ". So it's wrong to clear _PAGE_PRESENT,because this will make 
pmd_present=false.

On the other hand, There is no need to clear dirty flag too.

Thanks.