linux-kernel - Re: [Patch V5 13/16] xen: add explicit memblock

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Message-ID: <20150713140119.GD7125@l.oracle.com>
Date:	Mon, 13 Jul 2015 10:01:19 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Juergen Gross <jgross@...e.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	david.vrabel@...rix.com, boris.ostrovsky@...cle.com
Subject: Re: [Patch V5 13/16] xen: add explicit memblock_reserve() calls for
 special pages

On Mon, Jul 13, 2015 at 06:10:23AM +0200, Juergen Gross wrote:
> On 07/10/2015 03:36 PM, Konrad Rzeszutek Wilk wrote:
> >>diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> >>index 1982617..c28f7f7 100644
> >>--- a/arch/x86/xen/mmu.c
> >>+++ b/arch/x86/xen/mmu.c
> >>@@ -2084,6 +2084,19 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
> >>  }
> >>  #endif	/* CONFIG_X86_64 */
> >>
> >>+void __init xen_reserve_special_pages(void)
> >>+{
> >>+	phys_addr_t paddr;
> >>+
> >>+	memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
> >>+	if (!xen_initial_domain()) {
> >>+		paddr = PFN_PHYS(mfn_to_pfn(xen_start_info->store_mfn));
> >>+		memblock_reserve(paddr, PAGE_SIZE);
> >>+		paddr = PFN_PHYS(mfn_to_pfn(xen_start_info->console.domU.mfn));
> >>+		memblock_reserve(paddr, PAGE_SIZE);
> >>+	}
> >
> >I believe we can start an MiniOS as the 'dom0' (so first domain), and then
> >Linux right after as the 'dom1' (semi-dom0?). In which case XenStore would
> >be actually available.
> 
> And this dom1 would still be the "initial domain" (SIF_INITDOMAIN set)?

Yes.
> 
> I couldn't spot other Xen usage of this flag as the one in the
> hypervisor when constructing the "real" initial domain.
> 
> >Is there an way to figure out whether these mfns are valid and just
> >piggyback on that?
> 
> For store_mfn: yes (it's initialized to 0 by the hypervisor).

Excellent. Lets at least piggyback on that.
> 
> The console mfn: no, as the console info is a union which will hold
> different information in case of the initial domain.

OK.
> 
> 
> Juergen
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