linux-kernel - Re: [PATCH v1 04/12] xen/hvmlite: Bootstrap HVMlite guest

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Date:	Mon, 25 Jan 2016 22:12:03 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	david.vrabel@...rix.com, konrad.wilk@...cle.com,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	roger.pau@...rix.com, hpa@...or.com,
	Juergen Gross <jgross@...e.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...e.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH v1 04/12] xen/hvmlite: Bootstrap HVMlite guest

On Mon, Jan 25, 2016 at 11:08:47AM -0500, Boris Ostrovsky wrote:
> On 01/22/2016 06:32 PM, Luis R. Rodriguez wrote:
> >On Fri, Jan 22, 2016 at 04:35:50PM -0500, Boris Ostrovsky wrote:
> >
> >>+/*
> >>+ * This routine (and those that it might call) should not use
> >>+ * anything that lives in .bss since that segment will be cleared later
> >>+ */
> >>+void __init xen_prepare_hvmlite(void)
> >>+{
> >>+	u32 eax, ecx, edx, msr;
> >>+	u64 pfn;
> >>+
> >>+	cpuid(xen_cpuid_base() + 2, &eax, &msr, &ecx, &edx);
> >>+	pfn = __pa(hypercall_page);
> >>+	wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
> >>+
> >>+	pv_info.name = "Xen HVMlite";
> >>+	xen_domain_type = XEN_HVM_DOMAIN;
> >>+	xen_hvmlite = 1;
> >>+
> >>+	x86_init.oem.arch_setup = xen_init_kernel;
> >>+	x86_init.oem.banner = xen_banner;
> >>+
> >>+	hvmlite_bootparams();
> >>+}
> >>+#endif
> >If the boot_params.hdr.hardware_subarch_data pointed to a custom
> >struct then the first C entry point for Xen could shuffle this and
> >set this too, by still using less asm entry helpers. We'd still
> >need this run but with the linker table I think we could have
> >a stub small stub for hvm run, it would not be a call from asm.
> 
> Perhaps, but someone would still have to set hardware_subarch. And
> it's hvmlite_bootparams() that does it.

No, Xen would do it as well, essentially all of hvmlite_bootparams() could be
done in Xen.

> And that's not sufficient, I think. There are still some things that
> trampoline code sets up (e.g. page tables for 64-bit).

Sure, but only what is required, that should be rather smaller.

  Luis