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@xxxxxxxxxx>
> Fixes: c988cfd38e48 ("powerpc/32: use set_memory_attr()")
> Cc: stable@xxxxxxxxxxxxxxx
> Depends-on: 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against
> concurrent accesses")
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Reviewed-by: Russell Currey <ruscur@xxxxxxxxxx>
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
