Re: [PATCH v1 3/4] arm64: decouple check whether pfn is in linear map from pfn_valid()

Mike Rapoport
2021-04-21T05:33:08Z

On Tue, Apr 20, 2021 at 05:57:57PM +0200, David Hildenbrand wrote:
> On 20.04.21 11:09, Mike Rapoport wrote:
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > The intended semantics of pfn_valid() is to verify whether there is a
> > struct page for the pfn in question and nothing else.
> >
> > Yet, on arm64 it is used to distinguish memory areas that are mapped in the
> > linear map vs those that require ioremap() to access them.
> >
> > Introduce a dedicated pfn_is_map_memory() wrapper for
> > memblock_is_map_memory() to perform such check and use it where
> > appropriate.
> >
> > Using a wrapper allows to avoid cyclic include dependencies.
> >
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> > arch/arm64/include/asm/memory.h | 2 +-
> > arch/arm64/include/asm/page.h | 1 +
> > arch/arm64/kvm/mmu.c | 2 +-
> > arch/arm64/mm/init.c | 6 ++++++
> > arch/arm64/mm/ioremap.c | 4 ++--
> > arch/arm64/mm/mmu.c | 2 +-
> > 6 files changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> > index 0aabc3be9a75..194f9f993d30 100644
> > --- a/arch/arm64/include/asm/memory.h
> > +++ b/arch/arm64/include/asm/memory.h
> > @@ -351,7 +351,7 @@ static inline void *phys_to_virt(phys_addr_t x)
> > #define virt_addr_valid(addr) ({ \
> > __typeof__(addr) __addr = __tag_reset(addr); \
> > - __is_lm_address(__addr) && pfn_valid(virt_to_pfn(__addr)); \
> > + __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \
> > })
> > void dump_mem_limit(void);
> > diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
> > index 012cffc574e8..99a6da91f870 100644
> > --- a/arch/arm64/include/asm/page.h
> > +++ b/arch/arm64/include/asm/page.h
> > @@ -38,6 +38,7 @@ void copy_highpage(struct page *to, struct page *from);
> > typedef struct page *pgtable_t;
> > extern int pfn_valid(unsigned long);
> > +extern int pfn_is_map_memory(unsigned long);
> > #include <asm/memory.h>
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 8711894db8c2..23dd99e29b23 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -85,7 +85,7 @@ void kvm_flush_remote_tlbs(struct kvm *kvm)
> > static bool kvm_is_device_pfn(unsigned long pfn)
> > {
> > - return !pfn_valid(pfn);
> > + return !pfn_is_map_memory(pfn);
> > }
> > /*
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 3685e12aba9b..c54e329aca15 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -258,6 +258,12 @@ int pfn_valid(unsigned long pfn)
> > }
> > EXPORT_SYMBOL(pfn_valid);
> > +int pfn_is_map_memory(unsigned long pfn)
> > +{
>
> I think you might have to add (see pfn_valid())
>
> if (PHYS_PFN(PFN_PHYS(pfn)) != pfn)
> return 0;
>
> to catch false positives.

Yeah, makes sense.

> > + return memblock_is_map_memory(PFN_PHYS(pfn));
> > +}
> > +EXPORT_SYMBOL(pfn_is_map_memory);
> > +
> > static phys_addr_t memory_limit = PHYS_ADDR_MAX;
> > /*
> > diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
> > index b5e83c46b23e..b7c81dacabf0 100644
> > --- a/arch/arm64/mm/ioremap.c
> > +++ b/arch/arm64/mm/ioremap.c
> > @@ -43,7 +43,7 @@ static void __iomem *__ioremap_caller(phys_addr_t phys_addr, size_t size,
> > /*
> > * Don't allow RAM to be mapped.
> > */
> > - if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
> > + if (WARN_ON(pfn_is_map_memory(__phys_to_pfn(phys_addr))))
> > return NULL;
> > area = get_vm_area_caller(size, VM_IOREMAP, caller);
> > @@ -84,7 +84,7 @@ EXPORT_SYMBOL(iounmap);
> > void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size)
> > {
> > /* For normal memory we already have a cacheable mapping. */
> > - if (pfn_valid(__phys_to_pfn(phys_addr)))
> > + if (pfn_is_map_memory(__phys_to_pfn(phys_addr)))
> > return (void __iomem *)__phys_to_virt(phys_addr);
> > return __ioremap_caller(phys_addr, size, __pgprot(PROT_NORMAL),
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index 5d9550fdb9cf..26045e9adbd7 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -81,7 +81,7 @@ void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
> > pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
> > unsigned long size, pgprot_t vma_prot)
> > {
> > - if (!pfn_valid(pfn))
> > + if (!pfn_is_map_memory(pfn))
> > return pgprot_noncached(vma_prot);
> > else if (file->f_flags & O_SYNC)
> > return pgprot_writecombine(vma_prot);
> >
>
> As discussed, in the future it would be nice if we could just rely on the
> memmap state. There are cases where pfn_is_map_memory() will now be slower
> than pfn_valid() -- e.g., we don't check for valid_section() in case of
> CONFIG_SPARSEMEM. This would apply where pfn_valid() would have returned
> "0".
>
> As we're not creating the direct map, kern_addr_valid() shouldn't need love.
> It'd be some kind of ugly if some generic code used by arm64 would be
> relying in case of arm64 on pfn_valid() to return the expected result; I
> doubt it.

No doubt there is a room for further improvement in this area.

> Acked-by: David Hildenbrand <david@redhat.com>

Thanks!

--
Sincerely yours,
Mike.