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

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Date:   Thu, 25 Jan 2018 13:06:26 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Greg KH <gregkh@...uxfoundation.org>
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 25/01/18 12:00, Greg KH wrote:
> 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?

No, but as the build wouldn't break whenever this is changed I wanted
to make sure the symbol is found.

If you feel strong about that I can remove the EXPORT_SYMBOL_GPL().


Juergen