Re: [PATCH -next] powerpc/mm: check base flags in ioremap_prot
From: Christophe Leroy <hidden>
Date: 2021-09-03 09:17:18
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lkml
Le 03/09/2021 à 11:03, Nanyong Sun a écrit :
Some drivers who call ioremap_prot without setting base flags like
ioremap_prot(addr, len, 0) may work well before
commit 56f3c1413f5c ("powerpc/mm: properly set PAGE_KERNEL flags in
ioremap()"), but now they will get a virtual address "successfully"
from ioremap_prot and badly fault on memory access later because that
patch also dropped the hack adding of base flags for ioremap_prot.
So return NULL and throw a warning if the caller of ioremap_prot did
not set base flags properly. Why not just hack adding PAGE_KERNEL flags
in the ioremap_prot, because most scenarios can be covered by high level
functions like ioremap(), ioremap_coherent(), ioremap_cache()...
so it is better to keep max flexibility for this low level api.As far as I can see, there is no user of this fonction that sets flags to 0 in the kernel tree. Did you find any ? If you did, I think it is better to fix the caller. Christophe
quoted hunk ↗ jump to hunk
Signed-off-by: Nanyong Sun <redacted> --- arch/powerpc/mm/ioremap.c | 4 ++++ 1 file changed, 4 insertions(+)diff --git a/arch/powerpc/mm/ioremap.c b/arch/powerpc/mm/ioremap.c index 57342154d2b0..b7eda0f0d04d 100644 --- a/arch/powerpc/mm/ioremap.c +++ b/arch/powerpc/mm/ioremap.c@@ -46,6 +46,10 @@ void __iomem *ioremap_prot(phys_addr_t addr, unsigned long size, unsigned long f pte_t pte = __pte(flags); void *caller = __builtin_return_address(0); + /* The caller should set base page flags properly */ + if (WARN_ON((flags & _PAGE_PRESENT) == 0))
This probably doesn't work for some plateforms like book3s/64. You should use helpers like pte_present(). See the comment at https://elixir.bootlin.com/linux/v5.14/source/arch/powerpc/include/asm/book3s/64/pgtable.h#L591
+ return NULL; + /* writeable implies dirty for kernel addresses */ if (pte_write(pte)) pte = pte_mkdirty(pte);