Subject: Re: [PATCH v3 4/4] arch, mm: make kernel_page_present() always available

From: Mike Rapoport <[email-masked]>
Date: Mon, 2 Nov 2020 17:18:29 +0200

On Mon, Nov 02, 2020 at 10:28:14AM +0100, David Hildenbrand wrote:
> On 01.11.20 18:08, Mike Rapoport wrote:
> > From: Mike Rapoport <[email-masked]>
> > 
> > For architectures that enable ARCH_HAS_SET_MEMORY having the ability to
> > verify that a page is mapped in the kernel direct map can be useful
> > regardless of hibernation.
> > 
> > Add RISC-V implementation of kernel_page_present(), update its forward
> > declarations and stubs to be a part of set_memory API and remove ugly
> > ifdefery in inlcude/linux/mm.h around current declarations of
> > kernel_page_present().
> > 
> > Signed-off-by: Mike Rapoport <[email-masked]>
> > ---
> >   arch/arm64/include/asm/cacheflush.h |  1 +
> >   arch/arm64/mm/pageattr.c            |  4 +---
> >   arch/riscv/include/asm/set_memory.h |  1 +
> >   arch/riscv/mm/pageattr.c            | 29 +++++++++++++++++++++++++++++
> >   arch/x86/include/asm/set_memory.h   |  1 +
> >   arch/x86/mm/pat/set_memory.c        |  4 +---
> >   include/linux/mm.h                  |  7 -------
> >   include/linux/set_memory.h          |  5 +++++
> >   8 files changed, 39 insertions(+), 13 deletions(-)
> > 
> > diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
> > index 9384fd8fc13c..45217f21f1fe 100644
> > --- a/arch/arm64/include/asm/cacheflush.h
> > +++ b/arch/arm64/include/asm/cacheflush.h
> > @@ -140,6 +140,7 @@ int set_memory_valid(unsigned long addr, int numpages, int enable);
> >   int set_direct_map_invalid_noflush(struct page *page);
> >   int set_direct_map_default_noflush(struct page *page);
> > +bool kernel_page_present(struct page *page);
> >   #include <asm-generic/cacheflush.h>
> > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > index 439325532be1..92eccaf595c8 100644
> > --- a/arch/arm64/mm/pageattr.c
> > +++ b/arch/arm64/mm/pageattr.c
> > @@ -186,8 +186,8 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
> >   	set_memory_valid((unsigned long)page_address(page), numpages, enable);
> >   }
> > +#endif /* CONFIG_DEBUG_PAGEALLOC */
> > -#ifdef CONFIG_HIBERNATION
> >   /*
> >    * This function is used to determine if a linear map page has been marked as
> >    * not-valid. Walk the page table and check the PTE_VALID bit. This is based
> > @@ -234,5 +234,3 @@ bool kernel_page_present(struct page *page)
> >   	ptep = pte_offset_kernel(pmdp, addr);
> >   	return pte_valid(READ_ONCE(*ptep));
> >   }
> > -#endif /* CONFIG_HIBERNATION */
> > -#endif /* CONFIG_DEBUG_PAGEALLOC */
> > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > index 4c5bae7ca01c..d690b08dff2a 100644
> > --- a/arch/riscv/include/asm/set_memory.h
> > +++ b/arch/riscv/include/asm/set_memory.h
> > @@ -24,6 +24,7 @@ static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
> >   int set_direct_map_invalid_noflush(struct page *page);
> >   int set_direct_map_default_noflush(struct page *page);
> > +bool kernel_page_present(struct page *page);
> >   #endif /* __ASSEMBLY__ */
> > diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> > index 321b09d2e2ea..87ba5a68bbb8 100644
> > --- a/arch/riscv/mm/pageattr.c
> > +++ b/arch/riscv/mm/pageattr.c
> > @@ -198,3 +198,32 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
> >   			     __pgprot(0), __pgprot(_PAGE_PRESENT));
> >   }
> >   #endif
> > +
> > +bool kernel_page_present(struct page *page)
> > +{
> > +	unsigned long addr = (unsigned long)page_address(page);
> > +	pgd_t *pgd;
> > +	pud_t *pud;
> > +	p4d_t *p4d;
> > +	pmd_t *pmd;
> > +	pte_t *pte;
> > +
> > +	pgd = pgd_offset_k(addr);
> > +	if (!pgd_present(*pgd))
> > +		return false;
> > +
> > +	p4d = p4d_offset(pgd, addr);
> > +	if (!p4d_present(*p4d))
> > +		return false;
> > +
> > +	pud = pud_offset(p4d, addr);
> > +	if (!pud_present(*pud))
> > +		return false;
> > +
> > +	pmd = pmd_offset(pud, addr);
> > +	if (!pmd_present(*pmd))
> > +		return false;
> > +
> > +	pte = pte_offset_kernel(pmd, addr);
> > +	return pte_present(*pte);
> > +}
> > diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
> > index 5948218f35c5..4352f08bfbb5 100644
> > --- a/arch/x86/include/asm/set_memory.h
> > +++ b/arch/x86/include/asm/set_memory.h
> > @@ -82,6 +82,7 @@ int set_pages_rw(struct page *page, int numpages);
> >   int set_direct_map_invalid_noflush(struct page *page);
> >   int set_direct_map_default_noflush(struct page *page);
> > +bool kernel_page_present(struct page *page);
> >   extern int kernel_set_to_readonly;
> > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> > index bc9be96b777f..16f878c26667 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -2226,8 +2226,8 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
> >   	arch_flush_lazy_mmu_mode();
> >   }
> > +#endif /* CONFIG_DEBUG_PAGEALLOC */
> > -#ifdef CONFIG_HIBERNATION
> >   bool kernel_page_present(struct page *page)
> >   {
> >   	unsigned int level;
> > @@ -2239,8 +2239,6 @@ bool kernel_page_present(struct page *page)
> >   	pte = lookup_address((unsigned long)page_address(page), &level);
> >   	return (pte_val(*pte) & _PAGE_PRESENT);
> >   }
> > -#endif /* CONFIG_HIBERNATION */
> > -#endif /* CONFIG_DEBUG_PAGEALLOC */
> >   int __init kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
> >   				   unsigned numpages, unsigned long page_flags)
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index ab0ef6bd351d..44b82f22e76a 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2937,16 +2937,9 @@ static inline void debug_pagealloc_map_pages(struct page *page,
> >   	if (debug_pagealloc_enabled_static())
> >   		__kernel_map_pages(page, numpages, enable);
> >   }
> > -
> > -#ifdef CONFIG_HIBERNATION
> > -extern bool kernel_page_present(struct page *page);
> > -#endif	/* CONFIG_HIBERNATION */
> >   #else	/* CONFIG_DEBUG_PAGEALLOC */
> >   static inline void debug_pagealloc_map_pages(struct page *page,
> >   					     int numpages, int enable) {}
> > -#ifdef CONFIG_HIBERNATION
> > -static inline bool kernel_page_present(struct page *page) { return true; }
> > -#endif	/* CONFIG_HIBERNATION */
> >   #endif	/* CONFIG_DEBUG_PAGEALLOC */
> >   #ifdef __HAVE_ARCH_GATE_AREA
> > diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h
> > index 860e0f843c12..fe1aa4e54680 100644
> > --- a/include/linux/set_memory.h
> > +++ b/include/linux/set_memory.h
> > @@ -23,6 +23,11 @@ static inline int set_direct_map_default_noflush(struct page *page)
> >   {
> >   	return 0;
> >   }
> > +
> > +static inline bool kernel_page_present(struct page *page)
> > +{
> > +	return true;
> > +}
> >   #endif
> >   #ifndef set_mce_nospec
> > 
> 
> It's somewhat weird to move this to set_memory.h - it's only one possible
> user. I think include/linux/mm.h is a better fit. Ack to making it
> independent of CONFIG_HIBERNATION.

Semantically this is a part of direct map manipulation, that's primarily
why I put it into set_memory.h

> in include/linux/mm.h , I'd prefer:
> 
> #if defined(CONFIG_DEBUG_PAGEALLOC) || \
>     defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)

The second reason was to avoid this ^
and the third is -7 lines to include/linux/mm.h :)

> bool kernel_page_present(struct page *page);
> #else
> static inline bool kernel_page_present(struct page *page)
> {
> 	return true;
> }
> #endif
> 
> -- 
> Thanks,
> 
> David / dhildenb
> 
> 

-- 
Sincerely yours,
Mike.