linux-kernel - Re: [Xen-devel] [PATCH 2/3] x86/acpi: take rsdp address for boot params if available

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Date:   Tue, 28 Nov 2017 11:30:15 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Roger Pau Monné <roger.pau@...rix.com>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        x86@...nel.org, corbet@....net, rjw@...ysocki.net,
        linux-acpi@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
        boris.ostrovsky@...cle.com, tglx@...utronix.de, lenb@...nel.org
Subject: Re: [Xen-devel] [PATCH 2/3] x86/acpi: take rsdp address for boot
 params if available

On 28/11/17 11:18, Roger Pau Monné wrote:
> On Tue, Nov 28, 2017 at 10:43:59AM +0100, Juergen Gross wrote:
>> In case the rsdp address in struct boot_params is specified don't try
>> to find the table by searching, but take the address directly as set
>> by the boot loader.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>  drivers/acpi/osl.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
>> index 3bb46cb24a99..3b25e2ad7d75 100644
>> --- a/drivers/acpi/osl.c
>> +++ b/drivers/acpi/osl.c
>> @@ -45,6 +45,10 @@
>>  #include <linux/uaccess.h>
>>  #include <linux/io-64-nonatomic-lo-hi.h>
>>  
>> +#ifdef CONFIG_X86
>> +#include <asm/setup.h>
>> +#endif
>> +
>>  #include "internal.h"
>>  
>>  #define _COMPONENT		ACPI_OS_SERVICES
>> @@ -195,6 +199,10 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
>>  	if (acpi_rsdp)
>>  		return acpi_rsdp;
>>  #endif
>> +#ifdef CONFIG_X86
>> +	if (boot_params.hdr.acpi_rsdp_addr)
>> +		return boot_params.hdr.acpi_rsdp_addr;
>> +#endif
> 
> I'm struggling to figure out how was PVH getting the RSDP previously,
> because that should be removed now that it's in the zero-page.

I don't think it should be removed, because this was the legacy case
(searching through memory). It was pure luck that Xen put it at the
right location.


Juergen