linux-kernel - Re: [PATCH 2/3] xen: eliminate scalability issues from initrd handling

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Message-ID: <5408607F.6020108@citrix.com>
Date:	Thu, 4 Sep 2014 13:52:15 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>, <jbeulich@...e.com>
Subject: Re: [PATCH 2/3] xen: eliminate scalability issues from initrd handling

On 04/09/14 13:38, Juergen Gross wrote:
> Size restrictions native kernels wouldn't have resulted from the initrd
> getting mapped into the initial mapping. The kernel doesn't really need
> the initrd to be mapped, so use infrastructure available in Xen to avoid
> the mapping and hence the restriction.
[...]
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
[...]
> @@ -1667,10 +1668,20 @@ asmlinkage __visible void __init xen_start_kernel(void)
>  	new_cpu_data.x86_capability[0] = cpuid_edx(1);
>  #endif
>  
> +	if (xen_start_info->mod_start)
> +		initrd_start = __pa(xen_start_info->mod_start);
> +#ifdef CONFIG_BLK_DEV_INITRD
> +#ifdef CONFIG_X86_32
> +	BUG_ON(xen_start_info->flags & SIF_MOD_START_PFN);
> +#else
> +	if (xen_start_info->flags & SIF_MOD_START_PFN)
> +		initrd_start = PFN_PHYS(xen_start_info->mod_start);
> +#endif
> +#endif

Remove these unnecessary #ifdefs and the BUG_ON().  We can trust Xen to
not set SIF_MOD_START_PFN if we haven't asked for it.

> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -124,6 +124,9 @@ NEXT_HYPERCALL(arch_6)
>  	ELFNOTE(Xen, XEN_ELFNOTE_L1_MFN_VALID,
>  		.quad _PAGE_PRESENT; .quad _PAGE_PRESENT)
>  	ELFNOTE(Xen, XEN_ELFNOTE_SUSPEND_CANCEL, .long 1)
> +#ifdef CONFIG_X86_64
> +	ELFNOTE(Xen, XEN_ELFNOTE_MOD_START_PFN,  .long 1)
> +#endif

Why X86_64 only?  If there's a good reason the commit message needs to
explain why.

David
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