Re: [RFC PATCH v1 00/17] ban the use of _PAGE_XXX flags outside platform specific code
From: Christophe Leroy
Date: Fri Sep 07 2018 - 04:32:18 EST
On 09/06/2018 09:58 AM, Aneesh Kumar K.V wrote:
Christophe Leroy <christophe.leroy@xxxxxx> writes:
Today flags like for instance _PAGE_RW or _PAGE_USER are used through
common parts of code.
Using those directly in common parts of code have proven to lead to
mistakes or misbehaviour, because their use is not always as trivial
as one could think.
For instance, (flags & _PAGE_USER) == 0 isn't enough to tell
that a page is a kernel page, because some targets are using
_PAGE_PRIVILEDGED and not _PAGE_USER, so the test has to be
(flags & (_PAGE_USER | _PAGE_PRIVILEDGED)) == _PAGE_PRIVILEDGED
This has to (bad) consequences:
- All targets must define every bit, even the unsupported ones,
leading to a lot of useless #define _PAGE_XXX 0
- If someone forgets to take into account all possible _PAGE_XXX bits
for the case, we can get unexpected behaviour on some targets.
This becomes even more complex when we come to using _PAGE_RW.
Testing (flags & _PAGE_RW) is not enough to test whether a page
if writable or not, because:
- Some targets have _PAGE_RO instead, which has to be unset to tell
a page is writable
- Some targets have _PAGE_R and _PAGE_W, in which case
_PAGE_RW = _PAGE_R | _PAGE_W
- Even knowing whether a page is readable is not always trivial because:
- Some targets requires to check that _PAGE_R is set to ensure page
is readable
- Some targets requires to check that _PAGE_NA is not set
- Some targets requires to check that _PAGE_RO or _PAGE_RW is set
Etc ....
In order to work around all those issues and minimise the risks of errors,
this serie aims at removing all use of _PAGE_XXX flags from powerpc code
and always use pte_xxx() and pte_mkxxx() accessors instead. Those accessors
are then defined in target specific parts of the kernel code.
The series is really good. It also helps in code readability. Few things
i am not sure there is a way to reduce the overhead
- access = _PAGE_EXEC;
+ access = pte_val(pte_mkexec(__pte(0)));
Considering we have multiple big endian to little endian coversion there
for book3s 64.
Thanks for the review.
For the above, I propose the following:
diff --git a/arch/powerpc/mm/hash_utils_64.c
b/arch/powerpc/mm/hash_utils_64.c
index f23a89d8e4ce..904ac9c84ea5 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -1482,7 +1482,7 @@ static bool should_hash_preload(struct mm_struct
*mm, unsigned long ea)
#endif
void hash_preload(struct mm_struct *mm, unsigned long ea,
- unsigned long access, unsigned long trap)
+ bool is_exec, unsigned long trap)
{
int hugepage_shift;
unsigned long vsid;
@@ -1490,6 +1490,7 @@ void hash_preload(struct mm_struct *mm, unsigned
long ea,
pte_t *ptep;
unsigned long flags;
int rc, ssize, update_flags = 0;
+ unsigned long access = is_exec ? _PAGE_EXEC : 0;
BUG_ON(REGION_ID(ea) != USER_REGION_ID);
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 5c8530d0c611..4122f26a2f44 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -507,7 +507,8 @@ void update_mmu_cache(struct vm_area_struct *vma,
unsigned long address,
* We don't need to worry about _PAGE_PRESENT here because we are
* called with either mm->page_table_lock held or ptl lock held
*/
- unsigned long access, trap;
+ unsigned long trap;
+ bool is_exec;
if (radix_enabled()) {
prefetch((void *)address);
@@ -529,10 +530,10 @@ void update_mmu_cache(struct vm_area_struct *vma,
unsigned long address,
trap = current->thread.regs ? TRAP(current->thread.regs) : 0UL;
switch (trap) {
case 0x300:
- access = 0UL;
+ is_exec = false;
break;
case 0x400:
- access = _PAGE_EXEC;
+ is_exec = true;
break;
default:
return;
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index e5d779eed181..dd7f9b951d25 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -82,7 +82,7 @@ static inline void _tlbivax_bcast(unsigned long
address, unsigned int pid,
#else /* CONFIG_PPC_MMU_NOHASH */
extern void hash_preload(struct mm_struct *mm, unsigned long ea,
- unsigned long access, unsigned long trap);
+ bool is_exec, unsigned long trap);
extern void _tlbie(unsigned long address);
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index f983ffa24aa0..506e5c3e96da 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -263,7 +263,7 @@ static void __init __mapin_ram_chunk(unsigned long
offset, unsigned long top)
map_kernel_page(v, p, f);
#ifdef CONFIG_PPC_STD_MMU_32
if (ktext)
- hash_preload(&init_mm, v, 0, 0x300);
+ hash_preload(&init_mm, v, false, 0x300);
#endif
v += PAGE_SIZE;
p += PAGE_SIZE;
diff --git a/arch/powerpc/mm/ppc_mmu_32.c b/arch/powerpc/mm/ppc_mmu_32.c
index bea6c544e38f..38a793bfca37 100644
--- a/arch/powerpc/mm/ppc_mmu_32.c
+++ b/arch/powerpc/mm/ppc_mmu_32.c
@@ -163,7 +163,7 @@ void __init setbat(int index, unsigned long virt,
phys_addr_t phys,
* Preload a translation in the hash table
*/
void hash_preload(struct mm_struct *mm, unsigned long ea,
- unsigned long access, unsigned long trap)
+ bool is_exec, unsigned long trap)
{
pmd_t *pmd;
Other thing is __ioremap_at where we do
+ pte_t pte = __pte(flags);
/* Make sure we have the base flags */
- if ((flags & _PAGE_PRESENT) == 0)
+ if (!pte_present(pte))
This one is using pte_raw(), so shouldn't be a problem.
Since the function is doing almost nothing of on the flags, maybe
we could just replace the above by pte_present(__pte(flags)) and
leave the rest as is.
- err = map_kernel_page(v+i, p+i, flags);
+ err = map_kernel_page(v + i, p + i, pte_val(pte));
Maybe another alternative would be to pass a pte_t to map_kernel_page(),
then we have to find an optimised way to insert the RPN into it before
calling set_pte_at() instead of using pfn_pte() ?
If we are so concerned by the multiple conversions, should we modify all
the pte_mkxxxx() to use pte_raw() and __pte_raw() instead of pte_val()
and __pte() ?
But otherwise for the series.
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Thanks
Christophe