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

Xiao Guangrong
2010-07-03T08:24:18Z

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@cn.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