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

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Date:	Tue, 23 Jun 2015 15:49:49 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Julien Grall <julien.grall@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Russell King <linux@....linux.org.uk>,
	<ian.campbell@...rix.com>, <tim@....org>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 23/23] arm/xen: Add support for 64KB page granularity

On Tue, 23 Jun 2015, Julien Grall wrote:
> Hi,
> 
> On 23/06/15 15:19, Stefano Stabellini wrote:
> >> 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.
> 
> The implementation of xen_remap_domain_mfn_range return -ENOSYS no
> matter the page granularity.
> 
> This function is PV specific and has been added few months ago just for
> a stub. See comment in the code:
> "/* Not used by XENFEAT_auto_translated guests */"
> 
> Any logging/BUG_ON within this function is out of scope for this series.
> And I don't think this will be really useful. Feel free to send a patch
> for it.

Yes, you are right, I was reading an older version of Linux that still
had xen_remap_domain_mfn_range properly implemented.

The new function is called xen_remap_domain_mfn_array which calls
xen_xlate_remap_gfn_array.

I'll rephrase my question then: What about xen_remap_domain_mfn_array? 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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