On 20/11/17 02:53, Wanpeng Li wrote:
2017-11-18 5:03 GMT+08:00 Liran Alon <LIRAN.ALON@xxxxxxxxxx>:
On 17/11/17 23:01, Liran Alon wrote:
On 17/11/17 13:52, Dr. David Alan Gilbert (git) wrote:
From: "Dr. David Alan Gilbert" <dgilbert@xxxxxxxxxx>
In x2apic mode the LDR is fixed based on the ID rather
than separately loadable like it was before x2.
When kvm_apic_set_state is called, the base is set, and if
it has the X2APIC_ENABLE flag set then the LDR is calculated;
however that value gets overwritten by the memcpy a few lines
below overwriting it with the value that came from userland.
The symptom is a lack of EOI after loading the state
(e.g. after a QEMU migration) and is due to the EOI bitmap
being wrong due to the incorrect LDR. This was seen with
a Win2016 guest under Qemu with irqchip=split whose USB mouse
didn't work after a VM migration.
This corresponds to RH bug:
https://urldefense.proofpoint.com/v2/url?u=https-3A__bugzilla.redhat.com_show-5Fbug.cgi-3Fid-3D1502591&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=BDEsclkj9SNWbZXiuKgX07QVY0LqtwHA13yqtK4wreE&s=MJS_JxKV0dJS6T8qobO29j530xNJLFqgSuRMP8oEiwI&e=
Reported-by: Yiqian Wei <yiwei@xxxxxxxxxx>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
---
arch/x86/kvm/lapic.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 4991e9e51611..cff55beb0263 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2201,7 +2201,12 @@ static int kvm_apic_state_fixup(struct kvm_vcpu
*vcpu,
{
if (apic_x2apic_mode(vcpu->arch.apic)) {
u32 *id = (u32 *)(s->regs + APIC_ID);
+ u32 *ldr = (u32 *)(s->regs + APIC_LDR);
+ if (set) {
+ /* In x2 the LDR is fixed based on the id */
+ *ldr = kvm_apic_calc_x2apic_ldr(*id);
+ }
if (vcpu->kvm->arch.x2apic_format) {
if (*id != vcpu->vcpu_id)
return -EINVAL;
I think there is a bug here of not adding the new code in the right
place. I think diff should be instead:
@@ -2245,6 +2245,7 @@ static int kvm_apic_state_fixup(struct kvm_vcpu
*vcpu,
{
if (apic_x2apic_mode(vcpu->arch.apic)) {
u32 *id = (u32 *)(s->regs + APIC_ID);
+ u32 *ldr = (u32 *)(s->regs + APIC_LDR);
if (vcpu->kvm->arch.x2apic_format) {
if (*id != vcpu->vcpu_id)
@@ -2255,6 +2256,8 @@ static int kvm_apic_state_fixup(struct kvm_vcpu
*vcpu,
else
*id <<= 24;
}
+
+ *ldr = kvm_apic_calc_x2apic_ldr(*id);
}
return 0;
This is because of the x2apic_format hack.
(Fore more info, see commit 3713131345fb ("KVM: x86: add
KVM_CAP_X2APIC_API")).
Otherwise, you will use a value which can be shifted-left by 24.
-Liran
Sorry I meant diff should be:
@@ -2245,6 +2245,7 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
{
if (apic_x2apic_mode(vcpu->arch.apic)) {
u32 *id = (u32 *)(s->regs + APIC_ID);
+ u32 *ldr = (u32 *)(s->regs + APIC_LDR);
if (vcpu->kvm->arch.x2apic_format) {
if (*id != vcpu->vcpu_id)
@@ -2255,6 +2256,9 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
else
*id <<= 24;
}
+
+ if (set)
+ *ldr = kvm_apic_calc_x2apic_ldr(*id);
Why not move this to the else branch of vcpu->kvm->arch.x2apic_format
since LDR has already stored 32-bit logical x2APIC ID in x2apic mode?
First of all, I understand we agree that what I mentioned is indeed a
bug in original commit?
Second, if I understood original commit purpose correctly, you want to
make sure s->regs APIC_LDR value is correct and matches the s->regs
APIC_ID value. Instead of trusting userspace providing these values
synced correctly. Therefore, you should re-calc LDR regardless of if
x2apic_format was used by userspace or not.
BTW, I would expect that if this is the intent, there should also be a
commit which adds the "if (*id != vcpu->vcpu_id)" check to the case of
the non-x2apic_format after value was shifted-right by 24.
Regards,
-Liran
Regards,
Wanpeng Li
}
return 0;
