Re: [PATCH 08/15] powerpc/mm: Add new hash_page_mm()

Aneesh Kumar K.V
2014-09-29T08:51:05Z

Michael Neuling <mikey@neuling.org> writes:

> From: Ian Munsie <imunsie@au1.ibm.com>
>
> This adds a new function hash_page_mm() based on the existing hash_page().
> This version allows any struct mm to be passed in, rather than assuming
> current. This is useful for servicing co-processor faults which are not in the
> context of the current running process.
>
> We need to be careful here as the current hash_page() assumes current in a few
> places.

Can you also explain calling semantics. ie, why would we want to call
this with anything other than current ? Should we flush slb now or
should it be skipped ? so what would happen if the new hash page can
result in segment demotion ? You don't put that under if (mm ==
current->mm). is that ok ?

if ((pte_val(*ptep) & _PAGE_4K_PFN) && psize == MMU_PAGE_64K) {
demote_segment_4k(mm, ea);
psize = MMU_PAGE_4K;
}

We also update paca context there

if (get_paca_psize(addr) != MMU_PAGE_4K) {
get_paca()->context = mm->context;
slb_flush_and_rebolt();
}

You also added code to handle KERNEL_REGION_ID in
[PATCH 02/15] powerpc/cell: Move data segment faulting code out of cell
platform. do we need to handle that here ?

>
> Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> ---
> arch/powerpc/include/asm/mmu-hash64.h | 1 +
> arch/powerpc/mm/hash_utils_64.c | 20 +++++++++++++-------
> 2 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
> index fd19a53..a3b85e9 100644
> --- a/arch/powerpc/include/asm/mmu-hash64.h
> +++ b/arch/powerpc/include/asm/mmu-hash64.h
> @@ -319,6 +319,7 @@ extern int __hash_page_64K(unsigned long ea, unsigned long access,
> unsigned int local, int ssize);
> struct mm_struct;
> unsigned int hash_page_do_lazy_icache(unsigned int pp, pte_t pte, int trap);
> +extern int hash_page_mm(struct mm_struct *mm, unsigned long ea, unsigned long access, unsigned long trap);
> extern int hash_page(unsigned long ea, unsigned long access, unsigned long trap);
> int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
> pte_t *ptep, unsigned long trap, int local, int ssize,
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 0f73367..66071af 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -991,26 +991,24 @@ static void check_paca_psize(unsigned long ea, struct mm_struct *mm,
> * -1 - critical hash insertion error
> * -2 - access not permitted by subpage protection mechanism
> */
> -int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
> +int hash_page_mm(struct mm_struct *mm, unsigned long ea, unsigned long access, unsigned long trap)
> {
> enum ctx_state prev_state = exception_enter();
> pgd_t *pgdir;
> unsigned long vsid;
> - struct mm_struct *mm;
> pte_t *ptep;
> unsigned hugeshift;
> const struct cpumask *tmp;
> int rc, user_region = 0, local = 0;
> int psize, ssize;
>
> - DBG_LOW("hash_page(ea=%016lx, access=%lx, trap=%lx\n",
> - ea, access, trap);
> + DBG_LOW("%s(ea=%016lx, access=%lx, trap=%lx\n",
> + __func__, ea, access, trap);
>
> /* Get region & vsid */
> switch (REGION_ID(ea)) {
> case USER_REGION_ID:
> user_region = 1;
> - mm = current->mm;
> if (! mm) {
> DBG_LOW(" user region with no mm !\n");
> rc = 1;
> @@ -1106,7 +1104,8 @@ int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
> WARN_ON(1);
> }
> #endif
> - check_paca_psize(ea, mm, psize, user_region);
> + if (current->mm == mm)
> + check_paca_psize(ea, mm, psize, user_region);
>
> goto bail;
> }
> @@ -1149,7 +1148,8 @@ int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
> }
> }
>
> - check_paca_psize(ea, mm, psize, user_region);
> + if (current->mm == mm)
> + check_paca_psize(ea, mm, psize, user_region);
> #endif /* CONFIG_PPC_64K_PAGES */
>
> #ifdef CONFIG_PPC_HAS_HASH_64K
> @@ -1184,6 +1184,12 @@ bail:
> exception_exit(prev_state);
> return rc;
> }
> +EXPORT_SYMBOL_GPL(hash_page_mm);
> +
> +int hash_page(unsigned long ea, unsigned long access, unsigned long trap)
> +{
> + return hash_page_mm(current->mm, ea, access, trap);
> +}
> EXPORT_SYMBOL_GPL(hash_page);
>
> void hash_preload(struct mm_struct *mm, unsigned long ea,
> --
> 1.9.1
>
> --
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