WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] [PATCH 3 of 3] kexec: disable iommu jumping into the kdu

To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 3 of 3] kexec: disable iommu jumping into the kdump kernel
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Wed, 18 May 2011 16:57:19 -0400
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Wed, 18 May 2011 13:59:24 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4DD430A4.5000305@xxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <patchbomb.1305742093@andrewcoop> <aaf44d1a903dcb97b3ac.1305742096@andrewcoop> <20110518184946.GB14013@xxxxxxxxxxxx> <4DD430A4.5000305@xxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, May 18, 2011 at 09:48:36PM +0100, Andrew Cooper wrote:
> 
> 
> On 18/05/11 19:49, Konrad Rzeszutek Wilk wrote:
> >On Wed, May 18, 2011 at 07:08:16PM +0100, Andrew Cooper wrote:
> >>kdump kernels are unable to boot with IOMMU enabled,
> >>this patch disabled IOMMU mode and removes some of the generic
> >>code from the shutdown path which doesnt work after other
> >>CPUs have been shot down.
> >>
> >>Also, leave local interrupts disabled when jumping into pugatory
> >purgatory?
> purgatory is the bit of code which the a crashing kernel jumps into,
> which pretends to do minimal bootloader things to book the kdump
> kernel.  It is part of the kexec-tools package.

Ok. Might want to include that in the description.

> 
> >>as we have no idea whats in there and really dont want to be
> >>servicing interrupts when our entire state is invalid.
> >>
> >>Signed-off-by: Andrew Cooper<andrew.cooper3@xxxxxxxxxx>
> >>
> >>diff -r e80b5280fe2f -r aaf44d1a903d xen/arch/x86/crash.c
> >>--- a/xen/arch/x86/crash.c  Wed May 18 19:00:13 2011 +0100
> >>+++ b/xen/arch/x86/crash.c  Wed May 18 19:00:13 2011 +0100
> >>@@ -27,6 +27,8 @@
> >>  #include<asm/hvm/support.h>
> >>  #include<asm/apic.h>
> >>  #include<asm/io_apic.h>
> >>+#include<xen/iommu.h>
> >>+#include<asm/hvm/iommu.h>
> >>
> >>  static atomic_t waiting_for_crash_ipi;
> >>  static unsigned int crashing_cpu;
> >>@@ -43,7 +45,10 @@ static int crash_nmi_callback(struct cpu
> >>
> >>      kexec_crash_save_cpu();
> >>
> >>-    __stop_this_cpu();
> >>+    disable_local_APIC();
> >>+    hvm_cpu_down();
> >>+    clts();
> >>+    asm volatile ( "fninit" );
> >Can you provide a comment why you are using fninit and clt?
> >Is this what the Linux kernel does too when it goes through the kexec path?
> I was replacing __stop_this_cpu() with the safe subset of its
> contents - it was a verbatim copy minus the SMP stuff which the
> regular __stop_this_cpu() does.  I suppose I could have split
> __stop_this_cpu() to __crash_stop_this_cpu() but it didn't seem
> worth making such a trivially small function.

Why can't you use the SMP version? I know you are not running
in SMP mode, but does it hurt?

> >>
> >>      atomic_dec(&waiting_for_crash_ipi);
> >>
> >>@@ -56,6 +61,7 @@ static int crash_nmi_callback(struct cpu
> >>  static void nmi_shootdown_cpus(void)
> >>  {
> >>      unsigned long msecs;
> >>+    u64 msr_contents;
> >>
> >>      local_irq_disable();
> >>
> >>@@ -77,18 +83,43 @@ static void nmi_shootdown_cpus(void)
> >>          msecs--;
> >>      }
> >>
> >>-    __stop_this_cpu();
> >>+    disable_local_APIC();
> >>+    hvm_cpu_down();
> >>+    clts();
> >>+    asm volatile ( "fninit" );
> >>+
> >>+    /* This is a bit of a hack but there is no other way to shutdown 
> >>correctly
> >>+     * without a significant refactoring of the APIC code */
> >>+    rdmsrl(MSR_IA32_APICBASE, msr_contents);
> >>+    if ( cpu_has(&current_cpu_data, X86_FEATURE_X2APIC)
> >>+&&  (msr_contents&  MSR_IA32_APICBASE_EXTD) )
> >>+        x2apic_enabled = 1;
> >>+    else
> >>+        x2apic_enabled = 0;
> >>+
> >>      disable_IO_APIC();
> >>-
> >>-    local_irq_enable();
> >Why?
> Because that local_irq_enable() results in the interrupt flag being
> set when jumping into purgatory, which (at the moment) doesn't touch
> interrupts at all.  The result is that interrupts from PCI devices
> which are unaware of the crash are (potentially) being serviced by
> the xen handlers even though we have left the Xen context for good.

Yikes. Please do explain this in the code right there were you
remove the local_irq_enable..

> >>  }
> >>
> >>  void machine_crash_shutdown(void)
> >>  {
> >>      crash_xen_info_t *info;
> >>+    const struct iommu_ops * ops;
> >>
> >>      nmi_shootdown_cpus();
> >>
> >>+    /* Yes i know this is hacky but it is the easiest solution.  I should 
> >>add an iommu_ops
> >>+     * function called crash() or so which just disables the iommu 'fun' 
> >>without saving state
> >>+     */
> >>+    ops = iommu_get_ops();
> >>+    if(ops)
> >>+        ops->suspend();
> >Uh, no checking if ops->suspend exists?
> >
> True - at the moment both intel and amd iommu_ops are fully
> implemented but I will add an extra condition to the if statement.
> >>+
> >>+    /* Yes i know this is from driver/passthrough/vtd/ but it appears to 
> >>be architecture
> >>+     * independant, and also bears little/no relation to x2apic.  Needs 
> >>cleaning up
> >What about AMD VI IOMMUs? Does it work when that IOMMU is used?
> >
> It worked on the AMD box I tested the code on.  Like the comment
> says - as far as I can tell, it is architecture independent code.
> >>+     */
> >>+    iommu_disable_x2apic_IR();
> >Can't that function be done in the suspend code of the IOMMU?
> There is a comment in iommu suspend stating that it cant and isn't
> done, but rather is left for the local/ioapic_suspend functions
> which dont properly work in the kexec path.

OK, how about just moving it out of driver/passthrought/vtd then?

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>