Re: [PATCH v3 20/20] arm/xen: Add support for 64KB page granularity

[Stefano Stabellini]

On Fri, 7 Aug 2015, Julien Grall wrote:
> The hypercall interface is always using 4KB page granularity. This is
> requiring to use xen page definition macro when we deal with hypercall.
> 
> Note that pfn_to_gfn is working with a Xen pfn (i.e 4KB). We may want to
> rename pfn_gfn to make this explicit.
> 
> We also allocate a 64KB page for the shared page even though only the
> first 4KB is used. I don't think this is really important for now as it
> helps to have the pointer 4KB aligned (XENMEM_add_to_physmap is taking a
> Xen PFN).
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>

Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


> ---
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
> 
> Stefano, I've dropped your reviewed-by given I've updated the doc and do
> changes to avoid usage of XEN_PAGE_SHIFT
> 
>     Changes in v3:
>         - s/MFN/GFN/ base on the new naming
>         - Use virt_to_gfn to avoid use XEN_PAGE_SHIFT
>         - Drop Stefano's reviewed-by
>         - Add some docs in arch/arm/asm/xen/page.h
> 
>     Changes in v2
>         - Add Stefano's reviewed-by
> ---
>  arch/arm/include/asm/xen/page.h | 15 +++++++++++++--
>  arch/arm/xen/enlighten.c        |  6 +++---
>  2 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
> index 98c9fc3..e3d94cf 100644
> --- a/arch/arm/include/asm/xen/page.h
> +++ b/arch/arm/include/asm/xen/page.h
> @@ -28,6 +28,17 @@ typedef struct xpaddr {
>  
>  #define INVALID_P2M_ENTRY      (~0UL)
>  
> +/*
> + * The pseudo-physical frame (pfn) used in all the helpers is always based
> + * on Xen page granularity (i.e 4KB).
> + *
> + * A Linux page may be split across multiple non-contiguous Xen page so we
> + * have to keep track with frame based on 4KB page granularity.
> + *
> + * PV drivers should never make a direct usage of those helpers (particularly
> + * pfn_to_gfn and gfn_to_pfn).
> + */
> +
>  unsigned long __pfn_to_mfn(unsigned long pfn);
>  extern struct rb_root phys_to_mach;
>  
> @@ -64,8 +75,8 @@ static inline unsigned long bfn_to_pfn(unsigned long bfn)
>  #define bfn_to_local_pfn(bfn)	bfn_to_pfn(bfn)
>  
>  /* VIRT <-> GUEST conversion */
> -#define virt_to_gfn(v)		(pfn_to_gfn(virt_to_pfn(v)))
> -#define gfn_to_virt(m)		(__va(gfn_to_pfn(m) << PAGE_SHIFT))
> +#define virt_to_gfn(v)		(pfn_to_gfn(virt_to_phys(v) >> XEN_PAGE_SHIFT))
> +#define gfn_to_virt(m)		(__va(gfn_to_pfn(m) << XEN_PAGE_SHIFT))
>  
>  /* Only used in PV code. But ARM guests are always HVM. */
>  static inline xmaddr_t arbitrary_virt_to_machine(void *vaddr)
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index eeeab07..50b4769 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -89,8 +89,8 @@ static void xen_percpu_init(void)
>  	pr_info("Xen: initializing cpu%d\n", cpu);
>  	vcpup = per_cpu_ptr(xen_vcpu_info, cpu);
>  
> -	info.mfn = __pa(vcpup) >> PAGE_SHIFT;
> -	info.offset = offset_in_page(vcpup);
> +	info.mfn = virt_to_gfn(vcpup);
> +	info.offset = xen_offset_in_page(vcpup);
>  
>  	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
>  	BUG_ON(err);
> @@ -213,7 +213,7 @@ static int __init xen_guest_init(void)
>  	xatp.domid = DOMID_SELF;
>  	xatp.idx = 0;
>  	xatp.space = XENMAPSPACE_shared_info;
> -	xatp.gpfn = __pa(shared_info_page) >> PAGE_SHIFT;
> +	xatp.gpfn = virt_to_gfn(shared_info_page);
>  	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
>  		BUG();
>  
> -- 
> 2.1.4
> 
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