linux-kernel - [PATCH v2] KVM: IOAPIC: only access APIC registers one dword at a time

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Message-ID: <4C2D9C8C.8060401@cn.fujitsu.com>
Date:	Fri, 02 Jul 2010 16:00:12 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Jin Dongming <jin.dongming@...css.fujitsu.com>
Subject: [PATCH v2] KVM: IOAPIC: only access APIC registers one dword at a
 time

The IOAPIC spec says:

When accessing these registers, accesses must be done one dword at a time.
For example, software should never access byte 2 from the Data register before
accessing bytes 0 and 1. The hardware will not attempt to recover from a bad
programming model in this case.

So, this patch removes other width access

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 virt/kvm/ioapic.c |   20 +++++++-------------
 1 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 1149c60..6610d11 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -288,6 +288,11 @@ static int ioapic_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
 	ioapic_debug("addr %lx\n", (unsigned long)addr);
 	ASSERT(!(addr & 0xf));	/* check alignment */
 
+	if (len != 4) {
+		printk(KERN_WARNING "ioapic: wrong length %d\n", len);
+		return 0;
+	}
+
 	addr &= 0xff;
 	spin_lock(&ioapic->lock);
 	switch (addr) {
@@ -305,18 +310,7 @@ static int ioapic_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
 	}
 	spin_unlock(&ioapic->lock);
 
-	switch (len) {
-	case 8:
-		*(u64 *) val = result;
-		break;
-	case 1:
-	case 2:
-	case 4:
-		memcpy(val, (char *)&result, len);
-		break;
-	default:
-		printk(KERN_WARNING "ioapic: wrong length %d\n", len);
-	}
+	*(u32 *) val = result;
 	return 0;
 }
 
@@ -332,7 +326,7 @@ static int ioapic_mmio_write(struct kvm_io_device *this, gpa_t addr, int len,
 		     (void*)addr, len, val);
 	ASSERT(!(addr & 0xf));	/* check alignment */
 
-	if (len == 4 || len == 8)
+	if (len == 4)
 		data = *(u32 *) val;
 	else {
 		printk(KERN_WARNING "ioapic: Unsupported size %d\n", len);
-- 
1.6.1.2


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