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

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Date:   Thu, 25 Jan 2018 11:49:35 +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 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.


Juergen