On Fri, 2021-12-10 at 08:09 +0000, Christophe Leroy wrote:
set_memory_attr() was implemented by commit 4d1755b6a762 ("powerpc/mm: implement set_memory_attr()") because the set_memory_xx() couldn't be used at that time to modify memory "on the fly" as explained it the commit.
But set_memory_attr() uses set_pte_at() which leads to warnings when CONFIG_DEBUG_VM is selected, because set_pte_at() is unexpected for updating existing page table entries.
The check could be bypassed by using __set_pte_at() instead, as it was the case before commit c988cfd38e48 ("powerpc/32: use set_memory_attr()") but since commit 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against concurrent accesses") it is now possible to use set_memory_xx() functions to update page table entries "on the fly" because the update is now atomic.
For DEBUG_PAGEALLOC we need to clear and set back _PAGE_PRESENT. Add set_memory_np() and set_memory_p() for that.
Replace all uses of set_memory_attr() by the relevant set_memory_xx() and remove set_memory_attr().
Reported-by: Maxime Bizon mbizon@freebox.fr Fixes: c988cfd38e48 ("powerpc/32: use set_memory_attr()") Cc: stable@vger.kernel.org Depends-on: 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against concurrent accesses") Signed-off-by: Christophe Leroy christophe.leroy@csgroup.eu
Reviewed-by: Russell Currey ruscur@russell.cc
One comment below:
diff --git a/arch/powerpc/include/asm/set_memory.h b/arch/powerpc/include/asm/set_memory.h index b040094f7920..061f1766a8a4 100644 --- a/arch/powerpc/include/asm/set_memory.h +++ b/arch/powerpc/include/asm/set_memory.h @@ -6,6 +6,8 @@ #define SET_MEMORY_RW 1 #define SET_MEMORY_NX 2 #define SET_MEMORY_X 3 +#define SET_MEMORY_NP 4 +#define SET_MEMORY_P 5
It might be nice to have a comment somewhere in set_memory.h explaining that {p/np} = present/not present. RO/RW/NX/X are commonly used, "p" as shorthand for "present" is less obvious. x86's set_memory.h has a nice comment covering everything as an example.
int change_memory_attr(unsigned long addr, int numpages, long action); @@ -29,6 +31,14 @@ static inline int set_memory_x(unsigned long addr, int numpages) return change_memory_attr(addr, numpages, SET_MEMORY_X); } -int set_memory_attr(unsigned long addr, int numpages, pgprot_t prot); +static inline int set_memory_np(unsigned long addr, int numpages) +{ + return change_memory_attr(addr, numpages, SET_MEMORY_NP); +}
+static inline int set_memory_p(unsigned long addr, int numpages) +{ + return change_memory_attr(addr, numpages, SET_MEMORY_P); +} #endif