linux-kernel - Re: [PATCH 2/2] xen: add acpi_arch_get_root

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Date:   Thu, 25 Jan 2018 12:00:51 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        xen-devel@...ts.xenproject.org, lenb@...nel.org,
        rafael.j.wysocki@...el.com, mingo@...hat.com,
        boris.ostrovsky@...cle.com, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] xen: add acpi_arch_get_root_pointer() for pvh guests

On Thu, Jan 25, 2018 at 11:49:35AM +0100, Juergen Gross wrote:
> On 25/01/18 11:37, Greg KH wrote:
> > On Thu, Jan 25, 2018 at 11:04:54AM +0100, Juergen Gross wrote:
> >> Add acpi_arch_get_root_pointer() for Xen PVH guests to communicate
> >> the address of the RSDP table given to the kernel via Xen start info.
> >>
> >> This makes the kernel boot again in PVH mode after on recent Xen the
> >> RSDP was moved to higher addresses. So up to that change it was pure
> >> luck that the legacy method to locate the RSDP was working when
> >> running as PVH mode.
> >>
> >> Cc: <stable@...r.kernel.org> # 4.11
> >> Signed-off-by: Juergen Gross <jgross@...e.com>
> >> ---
> >>  arch/x86/xen/enlighten_pvh.c | 15 ++++++++++++---
> >>  1 file changed, 12 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
> >> index 436c4f003e17..9a5c3a7fe673 100644
> >> --- a/arch/x86/xen/enlighten_pvh.c
> >> +++ b/arch/x86/xen/enlighten_pvh.c
> >> @@ -16,15 +16,24 @@
> >>  /*
> >>   * PVH variables.
> >>   *
> >> - * xen_pvh and pvh_bootparams need to live in data segment since they
> >> - * are used after startup_{32|64}, which clear .bss, are invoked.
> >> + * xen_pvh, pvh_bootparams and pvh_start_info need to live in data segment
> >> + * since they are used after startup_{32|64}, which clear .bss, are invoked.
> >>   */
> >>  bool xen_pvh __attribute__((section(".data"))) = 0;
> >>  struct boot_params pvh_bootparams __attribute__((section(".data")));
> >> +struct hvm_start_info pvh_start_info __attribute__((section(".data")));
> >>  
> >> -struct hvm_start_info pvh_start_info;
> >>  unsigned int pvh_start_info_sz = sizeof(pvh_start_info);
> >>  
> >> +acpi_physical_address acpi_arch_get_root_pointer(void)
> >> +{
> >> +	if (xen_pvh)
> >> +		return pvh_start_info.rsdp_paddr;
> >> +
> >> +	return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(acpi_arch_get_root_pointer);
> > 
> > Why does this have to be an exported symbol?  Does this code get built
> > as a module and will the linker somehow go and rewrite the previous call
> > places with this one if it gets loaded?
> 
> With being called by drivers/acpi/... I just wanted to make sure it is
> working properly even in case the acpi code is built as a module.

I didn't think the core ACPI code can be built as a module, have you
tried that?

thanks,

greg k-h