Re: [PATCH] [v3] xen: avoid link error on ARM

[Stefano Stabellini <sstabellini@kernel.org>]

On Mon, 22 Jul 2019, Arnd Bergmann wrote:
> Building the privcmd code as a loadable module on ARM, we get
> a link error due to the private cache management functions:
> 
> ERROR: "__sync_icache_dcache" [drivers/xen/xen-privcmd.ko] undefined!
> 
> Move the code into a new that is always built in when Xen is enabled,
> as suggested by Juergen Gross and Boris Ostrovsky.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v2: rename mm.o to xen-builtin.o, make it unconditional
> v3: move new code into xlate_mmu as suggested by Boris Ostrovsky.
>     sorry for the long delay since v2, I lost track of this.
> ---
>  drivers/xen/privcmd.c   | 35 +++++------------------------------
>  drivers/xen/xlate_mmu.c | 32 ++++++++++++++++++++++++++++++++
>  include/xen/xen-ops.h   |  3 +++
>  3 files changed, 40 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 2f5ce7230a43..c6070e70dd73 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -724,25 +724,6 @@ static long privcmd_ioctl_restrict(struct file *file, void __user *udata)
>  	return 0;
>  }
>  
> -struct remap_pfn {
> -	struct mm_struct *mm;
> -	struct page **pages;
> -	pgprot_t prot;
> -	unsigned long i;
> -};
> -
> -static int remap_pfn_fn(pte_t *ptep, unsigned long addr, void *data)
> -{
> -	struct remap_pfn *r = data;
> -	struct page *page = r->pages[r->i];
> -	pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), r->prot));
> -
> -	set_pte_at(r->mm, addr, ptep, pte);
> -	r->i++;
> -
> -	return 0;
> -}
> -
>  static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
>  {
>  	struct privcmd_data *data = file->private_data;
> @@ -774,7 +755,8 @@ static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
>  		goto out;
>  	}
>  
> -	if (xen_feature(XENFEAT_auto_translated_physmap)) {
> +	if (IS_ENABLED(CONFIG_XEN_AUTO_XLATE) &&
> +	    xen_feature(XENFEAT_auto_translated_physmap)) {

The patch looks good. I tested it and works as intended. Instead of
adding the additional IS_ENABLED check, I would have gone with providing
an empty implementation of xen_remap_vma_range as a static inline
function, if CONFIG_XEN_AUTO_XLATE is not enabled.

Either way:

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


>  		unsigned int nr = DIV_ROUND_UP(kdata.num, XEN_PFN_PER_PAGE);
>  		struct page **pages;
>  		unsigned int i;
> @@ -808,16 +790,9 @@ static long privcmd_ioctl_mmap_resource(struct file *file, void __user *udata)
>  	if (rc)
>  		goto out;
>  
> -	if (xen_feature(XENFEAT_auto_translated_physmap)) {
> -		struct remap_pfn r = {
> -			.mm = vma->vm_mm,
> -			.pages = vma->vm_private_data,
> -			.prot = vma->vm_page_prot,
> -		};
> -
> -		rc = apply_to_page_range(r.mm, kdata.addr,
> -					 kdata.num << PAGE_SHIFT,
> -					 remap_pfn_fn, &r);
> +	if (IS_ENABLED(CONFIG_XEN_AUTO_XLATE) &&
> +	    xen_feature(XENFEAT_auto_translated_physmap)) {
> +		rc = xen_remap_vma_range(vma, kdata.addr, kdata.num << PAGE_SHIFT);
>  	} else {
>  		unsigned int domid =
>  			(xdata.flags & XENMEM_rsrc_acq_caller_owned) ?
> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> index ba883a80b3c0..7b1077f0abcb 100644
> --- a/drivers/xen/xlate_mmu.c
> +++ b/drivers/xen/xlate_mmu.c
> @@ -262,3 +262,35 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t **gfns, void **virt,
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(xen_xlate_map_ballooned_pages);
> +
> +struct remap_pfn {
> +	struct mm_struct *mm;
> +	struct page **pages;
> +	pgprot_t prot;
> +	unsigned long i;
> +};
> +
> +static int remap_pfn_fn(pte_t *ptep, unsigned long addr, void *data)
> +{
> +	struct remap_pfn *r = data;
> +	struct page *page = r->pages[r->i];
> +	pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), r->prot));
> +
> +	set_pte_at(r->mm, addr, ptep, pte);
> +	r->i++;
> +
> +	return 0;
> +}
> +
> +/* Used by the privcmd module, but has to be built-in on ARM */
> +int xen_remap_vma_range(struct vm_area_struct *vma, unsigned long addr, unsigned long len)
> +{
> +	struct remap_pfn r = {
> +		.mm = vma->vm_mm,
> +		.pages = vma->vm_private_data,
> +		.prot = vma->vm_page_prot,
> +	};
> +
> +	return apply_to_page_range(vma->vm_mm, addr, len, remap_pfn_fn, &r);
> +}
> +EXPORT_SYMBOL_GPL(xen_remap_vma_range);
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index 4969817124a8..98b30c1613b2 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -109,6 +109,9 @@ static inline int xen_xlate_unmap_gfn_range(struct vm_area_struct *vma,
>  }
>  #endif
>  
> +int xen_remap_vma_range(struct vm_area_struct *vma, unsigned long addr,
> +			unsigned long len);
> +
>  /*
>   * xen_remap_domain_gfn_array() - map an array of foreign frames by gfn
>   * @vma:     VMA to map the pages into
> -- 
> 2.20.0
>