Re: [PATCH v2] powerpc/32: Don't use a struct based type for pte_t
On Fri, 17 Sep 2021 15:57:31 +0200, Christophe Leroy wrote:
> Long time ago we had a config item called STRICT_MM_TYPECHECKS
> to build the kernel with pte_t defined as a structure in order
> to perform additional build checks or build it with pte_t
> defined as a simple type in order to get simpler generated code.
>
> Commit 670eea924198 ("powerpc/mm: Always use STRICT_MM_TYPECHECKS")
> made the struct based definition the only one, considering that the
> generated code was similar in both cases.
>
> [...]
Applied to powerpc/next.
[1/1] powerpc/32: Don't use a struct based type for pte_t
https://git.kernel.org/powerpc/c/c7d19189d7241e135cd2e450a7fbc77cb7bd40ee
cheers
Re: [PATCH v2] powerpc/32: Don't use a struct based type for pte_t
Le 17/09/2021 à 16:32, David Laight a écrit :
From: Christophe Leroy
Sent: 17 September 2021 14:58
Long time ago we had a config item called STRICT_MM_TYPECHECKS
to build the kernel with pte_t defined as a structure in order
to perform additional build checks or build it with pte_t
defined as a simple type in order to get simpler generated code.
...
diff --git a/arch/powerpc/include/asm/pgtable-types.h
b/arch/powerpc/include/asm/pgtable-types.h
index d11b4c61d686..c60199fc6fa6 100644
--- a/arch/powerpc/include/asm/pgtable-types.h
+++ b/arch/powerpc/include/asm/pgtable-types.h
@@ -5,14 +5,26 @@
/* PTE level */
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
-#else
+#elif defined(__CHECKER__) || !defined(CONFIG_PPC32)
typedef struct { pte_basic_t pte; } pte_t;
+#else
+typedef pte_basic_t pte_t;
#endif
+
+#if defined(__CHECKER__) || !defined(CONFIG_PPC32) || \
+(defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES))
#define __pte(x) ((pte_t) { (x) })
static inline pte_basic_t pte_val(pte_t x)
{
return x.pte;
}
+#else
+#define __pte(x) ((pte_t)(x))
+static inline pte_basic_t pte_val(pte_t x)
+{
+ return x;
+}
+#endif
Would it be better to define:
static inline pte_basic_*pte_basic(pte_t *x)
{
#if xxx
return x;
#else
return >pte;
#endif
}
Then pte_val(x) is always *pt_basic(x)
and the casts like:
- pte_basic_t *entry = >pte;
+ pte_basic_t *entry = (pte_basic_t *)ptep;
can go away.
I don't like that idea too much, because it means going through a
pointer of something which is not in memory at the begining. Doing that
forces GCC to put the pte_t object on stack. And that's exactly the
purpose of this patch: avoid having to go via memory. Allthough recent
versions of GCC optimise it away at the end, I don't like it in principle.
And the only two places (pte_update() and set_huge_pte_at() where this
cast is required are really two places very special which deal with real
page tables. So IMHO it makes sense to explicitely show that what we use
is the address of the entry in the page table.
Christophe
Re: [PATCH v2] powerpc/32: Don't use a struct based type for pte_t
Le 18/09/2021 à 05:26, Michael Ellerman a écrit :
Christophe Leroy writes:
Long time ago we had a config item called STRICT_MM_TYPECHECKS
to build the kernel with pte_t defined as a structure in order
to perform additional build checks or build it with pte_t
defined as a simple type in order to get simpler generated code.
Commit 670eea924198 ("powerpc/mm: Always use STRICT_MM_TYPECHECKS")
made the struct based definition the only one, considering that the
generated code was similar in both cases.
That's right on ppc64 because the ABI is such that the content of a
struct having a single simple type element is passed as register,
but on ppc32 such a structure is passed via the stack like any
structure.
Simple test function:
pte_t test(pte_t pte)
{
return pte;
}
Before this patch we get
c00108ec :
c00108ec: 81 24 00 00 lwz r9,0(r4)
c00108f0: 91 23 00 00 stw r9,0(r3)
c00108f4: 4e 80 00 20 blr
So, for PPC32, restore the simple type behaviour we got before
commit 670eea924198, but instead of adding a config option to
activate type check, do it when __CHECKER__ is set so that type
checking is performed by 'sparse' and provides feedback like:
arch/powerpc/mm/pgtable.c:466:16: warning: incorrect type in return
expression (different base types)
arch/powerpc/mm/pgtable.c:466:16:expected unsigned long
arch/powerpc/mm/pgtable.c:466:16:got struct pte_t [usertype] x
OK that's a good trade off.
One question below ...
diff --git a/arch/powerpc/include/asm/pgtable-types.h
b/arch/powerpc/include/asm/pgtable-types.h
index d11b4c61d686..c60199fc6fa6 100644
--- a/arch/powerpc/include/asm/pgtable-types.h
+++ b/arch/powerpc/include/asm/pgtable-types.h
@@ -5,14 +5,26 @@
/* PTE level */
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
-#else
+#elif defined(__CHECKER__) || !defined(CONFIG_PPC32)
It would be nicer if this logic was in Kconfig.
eg. restore config STRICT_MM_TYPECHECKS but make it always enabled for
64-bit, and depend on CHECKER for 32-bit.
The only thing is I'm not sure if we can test __CHECKER__ in Kconfig?
I think Kconfig doesn't see __CHECKER__, otherwise it would mean that a
build may get different whether you build with C=1/2 or not.
__CHECKER__ is a define added by sparse when doing the CHECK on a per
object basis.
What I can do is to add:
#if defined(__CHECKER__) || !defined(CONFIG_PPC32)
#define STRICT_MM_TYPECHECKS
#endif
Christophe
Re: [PATCH v2] powerpc/32: Don't use a struct based type for pte_t
Christophe Leroy writes:
> Long time ago we had a config item called STRICT_MM_TYPECHECKS
> to build the kernel with pte_t defined as a structure in order
> to perform additional build checks or build it with pte_t
> defined as a simple type in order to get simpler generated code.
>
> Commit 670eea924198 ("powerpc/mm: Always use STRICT_MM_TYPECHECKS")
> made the struct based definition the only one, considering that the
> generated code was similar in both cases.
>
> That's right on ppc64 because the ABI is such that the content of a
> struct having a single simple type element is passed as register,
> but on ppc32 such a structure is passed via the stack like any
> structure.
>
> Simple test function:
>
> pte_t test(pte_t pte)
> {
> return pte;
> }
>
> Before this patch we get
>
> c00108ec :
> c00108ec: 81 24 00 00 lwz r9,0(r4)
> c00108f0: 91 23 00 00 stw r9,0(r3)
> c00108f4: 4e 80 00 20 blr
>
> So, for PPC32, restore the simple type behaviour we got before
> commit 670eea924198, but instead of adding a config option to
> activate type check, do it when __CHECKER__ is set so that type
> checking is performed by 'sparse' and provides feedback like:
>
> arch/powerpc/mm/pgtable.c:466:16: warning: incorrect type in return
> expression (different base types)
> arch/powerpc/mm/pgtable.c:466:16:expected unsigned long
> arch/powerpc/mm/pgtable.c:466:16:got struct pte_t [usertype] x
OK that's a good trade off.
One question below ...
> diff --git a/arch/powerpc/include/asm/pgtable-types.h
> b/arch/powerpc/include/asm/pgtable-types.h
> index d11b4c61d686..c60199fc6fa6 100644
> --- a/arch/powerpc/include/asm/pgtable-types.h
> +++ b/arch/powerpc/include/asm/pgtable-types.h
> @@ -5,14 +5,26 @@
> /* PTE level */
> #if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
> -#else
> +#elif defined(__CHECKER__) || !defined(CONFIG_PPC32)
It would be nicer if this logic was in Kconfig.
eg. restore config STRICT_MM_TYPECHECKS but make it always enabled for
64-bit, and depend on CHECKER for 32-bit.
The only thing is I'm not sure if we can test __CHECKER__ in Kconfig?
cheers
RE: [PATCH v2] powerpc/32: Don't use a struct based type for pte_t
From: Christophe Leroy
> Sent: 17 September 2021 14:58
>
> Long time ago we had a config item called STRICT_MM_TYPECHECKS
> to build the kernel with pte_t defined as a structure in order
> to perform additional build checks or build it with pte_t
> defined as a simple type in order to get simpler generated code.
>
...
> diff --git a/arch/powerpc/include/asm/pgtable-types.h
> b/arch/powerpc/include/asm/pgtable-types.h
> index d11b4c61d686..c60199fc6fa6 100644
> --- a/arch/powerpc/include/asm/pgtable-types.h
> +++ b/arch/powerpc/include/asm/pgtable-types.h
> @@ -5,14 +5,26 @@
> /* PTE level */
> #if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
> -#else
> +#elif defined(__CHECKER__) || !defined(CONFIG_PPC32)
> typedef struct { pte_basic_t pte; } pte_t;
> +#else
> +typedef pte_basic_t pte_t;
> #endif
> +
> +#if defined(__CHECKER__) || !defined(CONFIG_PPC32) || \
> +(defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES))
> #define __pte(x) ((pte_t) { (x) })
> static inline pte_basic_t pte_val(pte_t x)
> {
> return x.pte;
> }
> +#else
> +#define __pte(x) ((pte_t)(x))
> +static inline pte_basic_t pte_val(pte_t x)
> +{
> + return x;
> +}
> +#endif
Would it be better to define:
static inline pte_basic_*pte_basic(pte_t *x)
{
#if xxx
return x;
#else
return >pte;
#endif
}
Then pte_val(x) is always *pt_basic(x)
and the casts like:
> - pte_basic_t *entry = >pte;
> + pte_basic_t *entry = (pte_basic_t *)ptep;
can go away.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)
[PATCH v2] powerpc/32: Don't use a struct based type for pte_t
Long time ago we had a config item called STRICT_MM_TYPECHECKS
to build the kernel with pte_t defined as a structure in order
to perform additional build checks or build it with pte_t
defined as a simple type in order to get simpler generated code.
Commit 670eea924198 ("powerpc/mm: Always use STRICT_MM_TYPECHECKS")
made the struct based definition the only one, considering that the
generated code was similar in both cases.
That's right on ppc64 because the ABI is such that the content of a
struct having a single simple type element is passed as register,
but on ppc32 such a structure is passed via the stack like any
structure.
Simple test function:
pte_t test(pte_t pte)
{
return pte;
}
Before this patch we get
c00108ec :
c00108ec: 81 24 00 00 lwz r9,0(r4)
c00108f0: 91 23 00 00 stw r9,0(r3)
c00108f4: 4e 80 00 20 blr
So, for PPC32, restore the simple type behaviour we got before
commit 670eea924198, but instead of adding a config option to
activate type check, do it when __CHECKER__ is set so that type
checking is performed by 'sparse' and provides feedback like:
arch/powerpc/mm/pgtable.c:466:16: warning: incorrect type in return
expression (different base types)
arch/powerpc/mm/pgtable.c:466:16:expected unsigned long
arch/powerpc/mm/pgtable.c:466:16:got struct pte_t [usertype] x
With this patch we now get
c0010890 :
c0010890: 4e 80 00 20 blr
Signed-off-by: Christophe Leroy
---
v2: Properly handle 8xx 16k pages
---
arch/powerpc/include/asm/nohash/32/pgtable.h | 2 +-
arch/powerpc/include/asm/pgtable-types.h | 14 +-
arch/powerpc/mm/pgtable.c| 2 +-
3 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/include/asm/nohash/32/pgtable.h
b/arch/powerpc/include/asm/nohash/32/pgtable.h
index f06ae00f2a65..34ce50da1850 100644
--- a/arch/powerpc/include/asm/nohash/32/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/32/pgtable.h
@@ -245,7 +245,7 @@ static int number_of_cells_per_pte(pmd_t *pmd, pte_basic_t
val, int huge)
static inline pte_basic_t pte_update(struct mm_struct *mm, unsigned long addr,
pte_t *p,
unsigned long clr, unsigned long set, int
huge)
{
- pte_basic_t *entry = >pte;
+ pte_basic_t *entry = (pte_basic_t *)p;
pte_basic_t old = pte_val(*p);
pte_basic_t new = (old & ~(pte_basic_t)clr) | set;
int num, i;
diff --git a/arch/powerpc/include/asm/pgtable-types.h
b/arch/powerpc/include/asm/pgtable-types.h
index d11b4c61d686..c60199fc6fa6 100644
--- a/arch/powerpc/include/asm/pgtable-types.h
+++ b/arch/powerpc/include/asm/pgtable-types.h
@@ -5,14 +5,26 @@
/* PTE level */
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
-#else
+#elif defined(__CHECKER__) || !defined(CONFIG_PPC32)
typedef struct { pte_basic_t pte; } pte_t;
+#else
+typedef pte_basic_t pte_t;
#endif
+
+#if defined(__CHECKER__) || !defined(CONFIG_PPC32) || \
+(defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES))
#define __pte(x) ((pte_t) { (x) })
static inline pte_basic_t pte_val(pte_t x)
{
return x.pte;
}
+#else
+#define __pte(x) ((pte_t)(x))
+static inline pte_basic_t pte_val(pte_t x)
+{
+ return x;
+}
+#endif
/* PMD level */
#ifdef CONFIG_PPC64
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index cd16b407f47e..ce9482383144 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -271,7 +271,7 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long
addr, pte_t *ptep, pte_
{
pmd_t *pmd = pmd_off(mm, addr);
pte_basic_t val;
- pte_basic_t *entry = >pte;
+ pte_basic_t *entry = (pte_basic_t *)ptep;
int num, i;
/*
--
2.31.1
