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

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Date:	Sat, 03 Jul 2010 16:20:27 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Jin Dongming <jin.dongming@...css.fujitsu.com>
Subject: Re: [PATCH v2] KVM: IOAPIC: only access APIC registers one dword
 at a time



Marcelo Tosatti wrote:

>> +	if (len != 4) {
>> +		printk(KERN_WARNING "ioapic: wrong length %d\n", len);
>> +		return 0;
>> +	}
>> +
> 
> Just remove the printks please, as guests can flood hosts dmesg.
> 

OK, please review this one, thanks, Marcelo!

Subject: [PATCH v3] 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 |   22 ++++++----------------
 1 files changed, 6 insertions(+), 16 deletions(-)

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 1149c60..aed91fd 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -288,6 +288,9 @@ 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)
+		return 0;
+
 	addr &= 0xff;
 	spin_lock(&ioapic->lock);
 	switch (addr) {
@@ -305,18 +308,7 @@ 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;
 }
 
@@ -332,12 +324,10 @@ 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);
+	else
 		return 0;
-	}
 
 	addr &= 0xff;
 	spin_lock(&ioapic->lock);
-- 
1.6.1.2

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