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 10:48:38 +0000
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Juergen Gross <jgross@...e.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 Tue, Nov 28, 2017 at 11:30:15AM +0100, Juergen Gross wrote:
> 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.

Oh, right. This is working out of pure luck then.

Thanks, Roger.