Re: [PATCH] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[Jane Chu <jane.chu@xxxxxxxxxx>]

On 4/8/2023 3:19 AM, Aneesh Kumar K.V wrote:
> Jane Chu <jane.chu@xxxxxxxxxx> writes:
>
> > On 4/7/2023 5:23 AM, Aneesh Kumar K.V wrote:
> > > diff --git a/mm/Kconfig b/mm/Kconfig
> > > index ff7b209dec05..99f87c1be1e8 100644
> > > --- a/mm/Kconfig
> > > +++ b/mm/Kconfig
> > > @@ -461,6 +461,9 @@ config SPARSEMEM_VMEMMAP
> > >    	  pfn_to_page and page_to_pfn operations.  This is the most
> > >    	  efficient option when sufficient kernel resources are available.
> > >    
> > > +config ARCH_WANT_OPTIMIZE_VMEMMAP
> > > +	bool
> > > +
> >
> > Could this devdax specific config switch be added to drivers/dax/Kconfig
> > ? also, how about adding 'DAX' to the config switch name?
>
> I would say we want to make it more generic. ie, both hugetlb and devdax
> can now derive the feature support via ARCH_WANT_OPTIMIZE_VMEMAP

The two config switches have different purposes, it's better to keep 
them separate.  For example, recent hugetlb high granularity mapping 
(HGM) project requires to users to make a choice between HGM and hugetlb 
vmemmap optimization(at least for now), while one can keep devdax 
compound page support enabled.

> commit aafb4790ea0250c8d2450e9d23a4be80c663d2ec
> Author: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Date:   Sat Apr 8 15:41:48 2023 +0530
>
>      mm/hugetlb: Remove ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>      
>      We can depend on the more generic ARCH_WACH_OPTIMIZE_VMEMAP
>      which is now used to enable both hugetlb and devddax vmemmap optimization.
>      
>      Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index d3f5945f0aff..77d9713dcd9c 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -100,7 +100,6 @@ config ARM64
>   	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>   	select ARCH_WANT_FRAME_POINTERS
>   	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>   	select ARCH_WANT_LD_ORPHAN_WARN
>   	select ARCH_WANTS_NO_INSTR
>   	select ARCH_WANT_OPTIMIZE_VMEMMAP
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index ce5802066d0e..9cb00f962de1 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -53,7 +53,6 @@ config LOONGARCH
>   	select ARCH_USE_QUEUED_RWLOCKS
>   	select ARCH_USE_QUEUED_SPINLOCKS
>   	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>   	select ARCH_WANT_LD_ORPHAN_WARN
>   	select ARCH_WANTS_NO_INSTR
>   	select ARCH_WANT_OPTIMIZE_VMEMMAP
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index abffccd937b2..df2cd510480a 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -126,7 +126,6 @@ config S390
>   	select ARCH_WANTS_NO_INSTR
>   	select ARCH_WANT_DEFAULT_BPF_JIT
>   	select ARCH_WANT_IPC_PARSE_VERSION
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>   	select ARCH_WANT_OPTIMIZE_VMEMMAP
>   	select BUILDTIME_TABLE_SORT
>   	select CLONE_BACKWARDS2
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index e8d66d834b4f..5269131cc248 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -125,7 +125,6 @@ config X86
>   	select ARCH_WANTS_NO_INSTR
>   	select ARCH_WANT_GENERAL_HUGETLB
>   	select ARCH_WANT_HUGE_PMD_SHARE
> -	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP	if X86_64
>   	select ARCH_WANT_LD_ORPHAN_WARN
>   	select ARCH_WANT_OPTIMIZE_VMEMMAP	if X86_64
>   	select ARCH_WANTS_THP_SWAP		if X86_64
> diff --git a/fs/Kconfig b/fs/Kconfig
> index e99830c65033..cc07a0cd3172 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -250,16 +250,9 @@ config HUGETLBFS
>   config HUGETLB_PAGE
>   	def_bool HUGETLBFS
>   
> -#
> -# Select this config option from the architecture Kconfig, if it is preferred
> -# to enable the feature of HugeTLB Vmemmap Optimization (HVO).
> -#
> -config ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> -	bool
> -
>   config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>   	def_bool HUGETLB_PAGE
> -	depends on ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> +	depends on ARCH_WANT_OPTIMIZE_VMEMMAP
>   	depends on SPARSEMEM_VMEMMAP
>   
>   config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 99f87c1be1e8..09ac60894763 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -460,7 +460,10 @@ config SPARSEMEM_VMEMMAP
>   	  SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
>   	  pfn_to_page and page_to_pfn operations.  This is the most
>   	  efficient option when sufficient kernel resources are available.
> -
> +#
> +# Select this config option from the architecture Kconfig, if it is preferred
> +# to enable the feature of HugeTLB/dev_dax vmemmap optimization.
> +#
>   config ARCH_WANT_OPTIMIZE_VMEMMAP
>   	bool
>   

thanks,
-jane