[PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[K. Y. Srinivasan]

Use the NULL legacy PIC when on Hyper-V. With this change we can support kexec
even when booting on EFI firmware. This patch has been tested on both EFI as
well as non-EFI firmware stacks on Hyper-V.

This patch is required to support kexec on EFI firmware on Hyper-V. Please
apply.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: <stable@vger.kernel.org>        [3.13+]
---
 arch/x86/kernel/cpu/mshyperv.c |   10 ++--------
 1 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 76f98fe..47359f7 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -133,14 +133,8 @@ static void __init ms_hyperv_init_platform(void)
 		printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
 				lapic_timer_frequency);
 
-		/*
-		 * On Hyper-V, when we are booting off an EFI firmware stack,
-		 * we do not have many legacy devices including PIC, PIT etc.
-		 */
-		if (efi_enabled(EFI_BOOT)) {
-			printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
-			legacy_pic = &null_legacy_pic;
-		}
+		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
+		legacy_pic = &null_legacy_pic;
 	}
 #endif
 
-- 
1.7.4.1

[tip:x86/hyperv] x86, hyperv: When on Hyper-v use NULL legacy PIC

[tip-bot for K. Y. Srinivasan]

Commit-ID:  8df28b82ff0649dd293f0469b97792cfb9ed10ab
Gitweb:     http://git.kernel.org/tip/8df28b82ff0649dd293f0469b97792cfb9ed10ab
Author:     K. Y. Srinivasan <kys@microsoft.com>
AuthorDate: Thu, 3 Apr 2014 18:16:33 -0700
Committer:  H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Thu, 3 Apr 2014 22:00:13 -0700

x86, hyperv: When on Hyper-v use NULL legacy PIC

Use the NULL legacy PIC when on Hyper-V. With this change we can support kexec
even when booting on EFI firmware. This patch has been tested on both EFI as
well as non-EFI firmware stacks on Hyper-V.

This patch is required to support kexec on EFI firmware on Hyper-V. Please
apply.

[ hpa: HyperV in EFI mode doesn't include a legacy PIC, and apparently
doesn't stub it out in a meaningful way.  This becomes an issue
after kexec if the second kernel doesn't know it is EFI-booted.
Since HyperV presumably never actually *needs* the legacy PIC, we
can just disable it. ]

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Link: http://lkml.kernel.org/r/1396574193-12043-1-git-send-email-kys@microsoft.com
Cc: <stable@vger.kernel.org>        [3.13+]
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
 arch/x86/kernel/cpu/mshyperv.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 832d05a..b7d82c7 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -93,14 +93,8 @@ static void __init ms_hyperv_init_platform(void)
 		printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
 				lapic_timer_frequency);
 
-		/*
-		 * On Hyper-V, when we are booting off an EFI firmware stack,
-		 * we do not have many legacy devices including PIC, PIT etc.
-		 */
-		if (efi_enabled(EFI_BOOT)) {
-			printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
-			legacy_pic = &null_legacy_pic;
-		}
+		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
+		legacy_pic = &null_legacy_pic;
 	}
 #endif
 

Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[Vivek Goyal]

On Thu, Apr 03, 2014 at 06:16:33PM -0700, K. Y. Srinivasan wrote:
> Use the NULL legacy PIC when on Hyper-V. With this change we can support kexec
> even when booting on EFI firmware. This patch has been tested on both EFI as
> well as non-EFI firmware stacks on Hyper-V.
> 
> This patch is required to support kexec on EFI firmware on Hyper-V. Please
> apply.

Can you give some more details about what's the problem we run into with
kexec on EFI on hyper-V.

Now EFI should be enabled in kexeced kernel. That means
efi_enabled(EFI_BOOT) should be true and that means you would set
legacy_pic to null anyway.

So with this patch, what changed w.r.t kexec on EFI.

Thansk
Vivek

> 
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> Cc: <stable@vger.kernel.org>        [3.13+]
> ---
>  arch/x86/kernel/cpu/mshyperv.c |   10 ++--------
>  1 files changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 76f98fe..47359f7 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -133,14 +133,8 @@ static void __init ms_hyperv_init_platform(void)
>  		printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
>  				lapic_timer_frequency);
>  
> -		/*
> -		 * On Hyper-V, when we are booting off an EFI firmware stack,
> -		 * we do not have many legacy devices including PIC, PIT etc.
> -		 */
> -		if (efi_enabled(EFI_BOOT)) {
> -			printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
> -			legacy_pic = &null_legacy_pic;
> -		}
> +		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
> +		legacy_pic = &null_legacy_pic;
>  	}
>  #endif
>  
> -- 
> 1.7.4.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

RE: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[KY Srinivasan]

> -----Original Message-----
> From: Vivek Goyal [mailto:vgoyal@redhat.com]
> Sent: Friday, April 4, 2014 7:12 AM
> To: KY Srinivasan
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com; hpa@zytor.com; KY Srinivasan;
> stable@vger.kernel.org
> Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL
> legacy PIC
> 
> On Thu, Apr 03, 2014 at 06:16:33PM -0700, K. Y. Srinivasan wrote:
> > Use the NULL legacy PIC when on Hyper-V. With this change we can
> > support kexec even when booting on EFI firmware. This patch has been
> > tested on both EFI as well as non-EFI firmware stacks on Hyper-V.
> >
> > This patch is required to support kexec on EFI firmware on Hyper-V.
> > Please apply.
> 
> Can you give some more details about what's the problem we run into with
> kexec on EFI on hyper-V.
> 
> Now EFI should be enabled in kexeced kernel. That means
> efi_enabled(EFI_BOOT) should be true and that means you would set
> legacy_pic to null anyway.
> 
> So with this patch, what changed w.r.t kexec on EFI.

Vivek,

On Hyper-V EFI firmware stack we have to set the legacy PIC to NULL legacy PIC since
legacy PIC is not emulated and if this were not set to NULL legacy PIC, we would crash in
PIC based calibration code. Hypervisor gives us the calibration information so
we don't need PIC based calibration.

Even on non-EFI firmware, the hypervisor gives us the calibration information
and so, we can set the legacy PIC to NULL legacy PIC unconditionally.

The problem we were having is that the initial boot on the EFI firmware
would succeed as the legacy PIC would be NULL legacy PIC, however
in the kexeced kernel, the initial boot information is not available and so
we would not set the legacy PIC to NULL legacy PIC. Thus, we would crash in
PIC based calibration code in the kexeced kernel.

Since we don't need legacy PIC both on EFI and non-EFI firmware,
we can set the legacy  PIC to NULL legacy PIC unconditionally.

K. Y 
> 
> Thansk
> Vivek
> 
> >
> > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> > Cc: <stable@vger.kernel.org>        [3.13+]
> > ---
> >  arch/x86/kernel/cpu/mshyperv.c |   10 ++--------
> >  1 files changed, 2 insertions(+), 8 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c
> > b/arch/x86/kernel/cpu/mshyperv.c index 76f98fe..47359f7 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -133,14 +133,8 @@ static void __init ms_hyperv_init_platform(void)
> >  		printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
> >  				lapic_timer_frequency);
> >
> > -		/*
> > -		 * On Hyper-V, when we are booting off an EFI firmware
> stack,
> > -		 * we do not have many legacy devices including PIC, PIT etc.
> > -		 */
> > -		if (efi_enabled(EFI_BOOT)) {
> > -			printk(KERN_INFO "HyperV: Using
> null_legacy_pic\n");
> > -			legacy_pic = &null_legacy_pic;
> > -		}
> > +		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
> > +		legacy_pic = &null_legacy_pic;
> >  	}
> >  #endif
> >
> > --
> > 1.7.4.1
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe
> > linux-kernel" in the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[Vivek Goyal]

On Fri, Apr 04, 2014 at 03:01:51PM +0000, KY Srinivasan wrote:

[..]
> The problem we were having is that the initial boot on the EFI firmware
> would succeed as the legacy PIC would be NULL legacy PIC, however
> in the kexeced kernel, the initial boot information is not available and so
> we would not set the legacy PIC to NULL legacy PIC.

I am curious to know what "initial boot information" is not available
in kexeced kernel and who is supposed to provide that.

Is it a bug or that's how it is supposed to work.

Thanks
Vivek

RE: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[KY Srinivasan]

> -----Original Message-----
> From: Vivek Goyal [mailto:vgoyal@redhat.com]
> Sent: Friday, April 4, 2014 8:16 AM
> To: KY Srinivasan
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com; hpa@zytor.com;
> stable@vger.kernel.org; Dave Young
> Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL
> legacy PIC
> 
> On Fri, Apr 04, 2014 at 03:01:51PM +0000, KY Srinivasan wrote:
> 
> [..]
> > The problem we were having is that the initial boot on the EFI
> > firmware would succeed as the legacy PIC would be NULL legacy PIC,
> > however in the kexeced kernel, the initial boot information is not
> > available and so we would not set the legacy PIC to NULL legacy PIC.
> 
> I am curious to know what "initial boot information" is not available in
> kexeced kernel and who is supposed to provide that.
> 
> Is it a bug or that's how it is supposed to work.

As the name indicates, the dump kernel is not "booted" but it is kexeced.
In the address space of this second kernel, the initial boot state is not visible.
This is the way it is supposed to work.

K. Y
> 
> Thanks
> Vivek

Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[Vivek Goyal]

On Fri, Apr 04, 2014 at 08:09:47PM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Vivek Goyal [mailto:vgoyal@redhat.com]
> > Sent: Friday, April 4, 2014 8:16 AM
> > To: KY Srinivasan
> > Cc: x86@kernel.org; linux-kernel@vger.kernel.org; olaf@aepfle.de;
> > apw@canonical.com; jasowang@redhat.com; hpa@zytor.com;
> > stable@vger.kernel.org; Dave Young
> > Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL
> > legacy PIC
> > 
> > On Fri, Apr 04, 2014 at 03:01:51PM +0000, KY Srinivasan wrote:
> > 
> > [..]
> > > The problem we were having is that the initial boot on the EFI
> > > firmware would succeed as the legacy PIC would be NULL legacy PIC,
> > > however in the kexeced kernel, the initial boot information is not
> > > available and so we would not set the legacy PIC to NULL legacy PIC.
> > 
> > I am curious to know what "initial boot information" is not available in
> > kexeced kernel and who is supposed to provide that.
> > 
> > Is it a bug or that's how it is supposed to work.
> 
> As the name indicates, the dump kernel is not "booted" but it is kexeced.
> In the address space of this second kernel, the initial boot state is not visible.

What do you mean by "initial boot state"? Most of the state we pass to
second kernel in bootparams and on command line and rest second kernel
can query from firmware as needed.

Thanks
Vivek

RE: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[KY Srinivasan]

> -----Original Message-----
> From: Vivek Goyal [mailto:vgoyal@redhat.com]
> Sent: Friday, April 4, 2014 1:32 PM
> To: KY Srinivasan
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com; hpa@zytor.com;
> stable@vger.kernel.org; Dave Young
> Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL
> legacy PIC
> 
> On Fri, Apr 04, 2014 at 08:09:47PM +0000, KY Srinivasan wrote:
> >
> >
> > > -----Original Message-----
> > > From: Vivek Goyal [mailto:vgoyal@redhat.com]
> > > Sent: Friday, April 4, 2014 8:16 AM
> > > To: KY Srinivasan
> > > Cc: x86@kernel.org; linux-kernel@vger.kernel.org; olaf@aepfle.de;
> > > apw@canonical.com; jasowang@redhat.com; hpa@zytor.com;
> > > stable@vger.kernel.org; Dave Young
> > > Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use
> > > NULL legacy PIC
> > >
> > > On Fri, Apr 04, 2014 at 03:01:51PM +0000, KY Srinivasan wrote:
> > >
> > > [..]
> > > > The problem we were having is that the initial boot on the EFI
> > > > firmware would succeed as the legacy PIC would be NULL legacy PIC,
> > > > however in the kexeced kernel, the initial boot information is not
> > > > available and so we would not set the legacy PIC to NULL legacy PIC.
> > >
> > > I am curious to know what "initial boot information" is not
> > > available in kexeced kernel and who is supposed to provide that.
> > >
> > > Is it a bug or that's how it is supposed to work.
> >
> > As the name indicates, the dump kernel is not "booted" but it is kexeced.
> > In the address space of this second kernel, the initial boot state is not
> visible.
> 
> What do you mean by "initial boot state"? Most of the state we pass to
> second kernel in bootparams and on command line and rest second kernel
> can query from firmware as needed.
Specifically, this check I had:
if (efi_enabled(EFI_BOOT)) {
}

Fails in the kexeced kernel even when running on EFI firmware.

K. Y

Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[Olaf Hering]

On Thu, Apr 03, K. Y. Srinivasan wrote:

> +		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");

Maybe this printk can be removed as well, unless its valuable info.

Olaf

RE: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[KY Srinivasan]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 738 bytes --]



> -----Original Message-----
> From: Olaf Hering [mailto:olaf@aepfle.de]
> Sent: Monday, April 7, 2014 12:06 AM
> To: KY Srinivasan
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; apw@canonical.com;
> jasowang@redhat.com; hpa@zytor.com; stable@vger.kernel.org
> Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL
> legacy PIC
> 
> On Thu, Apr 03, K. Y. Srinivasan wrote:
> 
> > +		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
> 
> Maybe this printk can be removed as well, unless its valuable info.

I will take a look at this.

K. Y
> 
> Olaf
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

RE: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL legacy PIC

[KY Srinivasan]

> -----Original Message-----
> From: Olaf Hering [mailto:olaf@aepfle.de]
> Sent: Monday, April 7, 2014 12:06 AM
> To: KY Srinivasan
> Cc: x86@kernel.org; linux-kernel@vger.kernel.org; apw@canonical.com;
> jasowang@redhat.com; hpa@zytor.com; stable@vger.kernel.org
> Subject: Re: [PATCH 1/1] x86/platform/hyperv: When on Hyper-v use NULL
> legacy PIC
> 
> On Thu, Apr 03, K. Y. Srinivasan wrote:
> 
> > +		printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
> 
> Maybe this printk can be removed as well, unless its valuable info.

I will take a look at this.

K. Y
> 
> Olaf