Re: [Xen-ia64-devel] [PATCH] zero extend I/O reads

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Hi Alex.

I digged into log and found the two commits as below.
I think they fixed the issue. So I guess you encountered
the issue before committing the c/s 16180:62a7a2f4d9c7.
They are several mounths before, so memory might be vague...


changeset:   16284:7eb68d995aa7
user:        Keir Fraser <keir@xxxxxxxxxxxxx>
date:        Tue Oct 30 16:25:58 2007 +0000
files:       xen/arch/ia64/vmx/mmio.c
description:
ia64: Fix after stdvga performance changes to bufioreq struct.
Signed-off-by: Alex Williamson <alex.williamson@xxxxxx>

--

changeset:   16180:62a7a2f4d9c7
user:        Alex Williamson <alex.williamson@xxxxxx>
date:        Mon Oct 22 12:30:17 2007 -0600
files:       xen/arch/ia64/vmx/mmio.c
description:
[IA64] Fix MMIO readb operation

We should do clean before read operation.  Otherwise, read one byte
data may get garbage data sometimes.

Signed-off-by: Zhang Xin <xing.z.zhang@xxxxxxxxx>


diff -r ecbda3783c85 -r 62a7a2f4d9c7 xen/arch/ia64/vmx/mmio.c
--- a/xen/arch/ia64/vmx/mmio.c  Mon Oct 22 12:26:53 2007 -0600
+++ b/xen/arch/ia64/vmx/mmio.c  Mon Oct 22 12:30:17 2007 -0600
@@ -120,6 +120,8 @@
     p->dir = dir;
     if (dir==IOREQ_WRITE)     // write;
         p->data = *val;
+    else if (dir == IOREQ_READ)
+        p->data = 0;          // clear all bits
     p->data_is_ptr = 0;
     p->type = 1;
     p->df = 0;


On Wed, May 21, 2008 at 01:17:24PM -0600, Alex Williamson wrote:
> 
> Jes Sorensen debugged an issue recently on KVM that a ld2.acq was
> getting sign extended in the I/O emulation path[1][2].  This was exposed
> by the VGA console hanging due to some benign looking changes to the VGA
> console structure several kernel revisions back.  I remember seeing this
> on Xen, but I've lost the recipe to reproduce it.  I believe the
> following patch adds the same logic that is being incorporated for KVM,
> but I'm unable to prove we're hitting the same issue since I can no
> longer reproduce it.  Please review and apply if it looks right.
> Thanks,
> 
>       Alex
> 
> [1] http://marc.info/?t=121118934000001
> [2] http://marc.info/?t=121127848500008
> 
> [IA64] zero pad emulated I/O instructions
> 
> Fixes issue seen on KVM with more recent upstream changes to the VGA
> console structure.
> 
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxx>
> 

-- 
yamahata

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