linux-kernel - [PATCH v3 2/3] KVM: LAPIC: Set the TDCR settable bits

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Date:   Fri, 31 Jul 2020 11:12:20 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH v3 2/3] KVM: LAPIC: Set the TDCR settable bits

From: Wanpeng Li <wanpengli@...cent.com>

It is a little different between Intel and AMD, Intel's bit 2
is 0 and AMD is reserved. On bare-metal, Intel will refuse to set
APIC_TDCR once bits except 0, 1, 3 are setting, however, AMD will
accept bits 0, 1, 3 and ignore other bits setting as patch does.
Before the patch, we can get back anything what we set to the
APIC_TDCR, this patch improves it.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
v1 -> v2:
 * update patch description

 arch/x86/kvm/lapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 4ce2ddd..8f7a14d 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2068,7 +2068,7 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 	case APIC_TDCR: {
 		uint32_t old_divisor = apic->divide_count;
 
-		kvm_lapic_set_reg(apic, APIC_TDCR, val);
+		kvm_lapic_set_reg(apic, APIC_TDCR, val & 0xb);
 		update_divide_count(apic);
 		if (apic->divide_count != old_divisor &&
 				apic->lapic_timer.period) {
-- 
2.7.4