linux-kernel - Re: [RFC 23/23] arm/xen: Add support for 64KB page granularity

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Message-ID: <alpine.DEB.2.02.1506231508050.16917@kaball.uk.xensource.com>
Date:	Tue, 23 Jun 2015 15:19:09 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Julien Grall <julien.grall@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>,
	<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	<tim@....org>, Russell King <linux@....linux.org.uk>
Subject: Re: [RFC 23/23] arm/xen: Add support for 64KB page granularity

On Thu, 14 May 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_mfn is working with a Xen pfn (i.e 4KB). We may want to
> rename pfn_mfn 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@...rix.com>
> Cc: Stefano Stabellini <stefano.stabellini@...citrix.com>
> Cc: Russell King <linux@....linux.org.uk>
>
>  arch/arm/include/asm/xen/page.h | 12 ++++++------
>  arch/arm/xen/enlighten.c        |  6 +++---
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
> index 1bee8ca..ab6eb9a 100644
> --- a/arch/arm/include/asm/xen/page.h
> +++ b/arch/arm/include/asm/xen/page.h
> @@ -56,19 +56,19 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
>  
>  static inline xmaddr_t phys_to_machine(xpaddr_t phys)
>  {
> -	unsigned offset = phys.paddr & ~PAGE_MASK;
> -	return XMADDR(PFN_PHYS(pfn_to_mfn(PFN_DOWN(phys.paddr))) | offset);
> +	unsigned offset = phys.paddr & ~XEN_PAGE_MASK;
> +	return XMADDR(XEN_PFN_PHYS(pfn_to_mfn(XEN_PFN_DOWN(phys.paddr))) | offset);
>  }
>  
>  static inline xpaddr_t machine_to_phys(xmaddr_t machine)
>  {
> -	unsigned offset = machine.maddr & ~PAGE_MASK;
> -	return XPADDR(PFN_PHYS(mfn_to_pfn(PFN_DOWN(machine.maddr))) | offset);
> +	unsigned offset = machine.maddr & ~XEN_PAGE_MASK;
> +	return XPADDR(XEN_PFN_PHYS(mfn_to_pfn(XEN_PFN_DOWN(machine.maddr))) | offset);
>  }
>  /* VIRT <-> MACHINE conversion */
>  #define virt_to_machine(v)	(phys_to_machine(XPADDR(__pa(v))))
> -#define virt_to_mfn(v)		(pfn_to_mfn(virt_to_pfn(v)))
> -#define mfn_to_virt(m)		(__va(mfn_to_pfn(m) << PAGE_SHIFT))
> +#define virt_to_mfn(v)		(pfn_to_mfn(virt_to_phys(v) >> XEN_PAGE_SHIFT))
> +#define mfn_to_virt(m)		(__va(mfn_to_pfn(m) << XEN_PAGE_SHIFT))
>  
>  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 224081c..dcfe251 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -93,8 +93,8 @@ 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 = __pa(vcpup) >> XEN_PAGE_SHIFT;
> +	info.offset = xen_offset_in_page(vcpup);
>  
>  	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
>  	BUG_ON(err);
> @@ -204,7 +204,7 @@ 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 = __pa(shared_info_page) >> XEN_PAGE_SHIFT;
>  	if (HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp))
>  		BUG();

What about xen_remap_domain_mfn_range? I guess we don't support that use
case on 64K guests? If so, I would appreaciate an assert and/or an error
message.
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