0010-x86-emul-Fix-misaligned-IO-breakpoint-behaviour-in-P.patch


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From 033060ee6e05f9e86ef1a51674864b55dc15e62c Mon Sep 17 00:00:00 2001
From: Matthew Barnes <matthew.barnes@cloud.com>
Date: Thu, 8 Aug 2024 13:48:03 +0200
Subject: [PATCH 10/35] x86/emul: Fix misaligned IO breakpoint behaviour in PV
 guests

When hardware breakpoints are configured on misaligned IO ports, the
hardware will mask the addresses based on the breakpoint width during
comparison.

For PV guests, misaligned IO breakpoints do not behave the same way, and
therefore yield different results.

This patch tweaks the emulation of IO breakpoints for PV guests such
that they reproduce the same behaviour as hardware.

Fixes: bec9e3205018 ("x86: emulate I/O port access breakpoints")
Signed-off-by: Matthew Barnes <matthew.barnes@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 08aacc392d86d4c7dbebdb5e664060ae2af72057
master date: 2024-08-08 13:27:50 +0200
---
 xen/arch/x86/pv/emul-priv-op.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index f101510a1b..aa11ecadaa 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -346,6 +346,8 @@ static unsigned int check_guest_io_breakpoint(struct vcpu *v,
         case DR_LEN_8: width = 8; break;
         }
 
+        start &= ~(width - 1UL);
+
         if ( (start < (port + len)) && ((start + width) > port) )
             match |= 1u << i;
     }
-- 
2.46.1