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Date: Fri, 14 Jan 2022 17:34:13 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Zeng Guang <guang.zeng@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"Luck, Tony" <tony.luck@...el.com>,
Kan Liang <kan.liang@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Kim Phillips <kim.phillips@....com>,
Jarkko Sakkinen <jarkko@...nel.org>,
Jethro Beekman <jethro@...tanix.com>,
"Huang, Kai" <kai.huang@...el.com>,
"x86@...nel.org" <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Hu, Robert" <robert.hu@...el.com>,
"Gao, Chao" <chao.gao@...el.com>
Subject: Re: [PATCH v5 5/8] KVM: x86: Support interrupt dispatch in x2APIC
mode with APIC-write VM exit
On Fri, Jan 14, 2022, Zeng Guang wrote:
> kvm_lapic_reg_read() is limited to read up to 4 bytes. It needs extension to
> support 64bit read.
Ah, right.
> And another concern is here getting reg value only specific from vICR(no
> other regs need take care), going through whole path on kvm_lapic_reg_read()
> could be time-consuming unnecessarily. Is it proper that calling
> kvm_lapic_get_reg64() to retrieve vICR value directly?
Hmm, no, I don't think that's proper. Retrieving a 64-bit value really is unique
to vICR. Yes, the code does WARN on that, but if future architectural extensions
even generate APIC-write exits on other registers, then using kvm_lapic_get_reg64()
would be wrong and this code would need to be updated again.
What about tweaking my prep patch from before to the below? That would yield:
if (apic_x2apic_mode(apic)) {
if (WARN_ON_ONCE(offset != APIC_ICR))
return 1;
kvm_lapic_msr_read(apic, offset, &val);
kvm_lapic_msr_write(apic, offset, val);
} else {
kvm_lapic_reg_read(apic, offset, 4, &val);
kvm_lapic_reg_write(apic, offset, val);
}
I like that the above has "msr" in the low level x2apic helpers, and it maximizes
code reuse. Compile tested only...
From: Sean Christopherson <seanjc@...gle.com>
Date: Fri, 14 Jan 2022 09:29:34 -0800
Subject: [PATCH] KVM: x86: Add helpers to handle 64-bit APIC MSR read/writes
Add helpers to handle 64-bit APIC read/writes via MSRs to deduplicate the
x2APIC and Hyper-V code needed to service reads/writes to ICR. Future
support for IPI virtualization will add yet another path where KVM must
handle 64-bit APIC MSR reads/write (to ICR).
Opportunistically fix the comment in the write path; ICR2 holds the
destination (if there's no shorthand), not the vector.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/kvm/lapic.c | 59 ++++++++++++++++++++++----------------------
1 file changed, 29 insertions(+), 30 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index f206fc35deff..cc4531eb448f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2787,6 +2787,30 @@ int kvm_lapic_set_vapic_addr(struct kvm_vcpu *vcpu, gpa_t vapic_addr)
return 0;
}
+static int kvm_lapic_msr_read(struct kvm_lapic *apic, u32 reg, u64 *data)
+{
+ u32 low, high = 0;
+
+ if (kvm_lapic_reg_read(apic, reg, 4, &low))
+ return 1;
+
+ if (reg == APIC_ICR &&
+ WARN_ON_ONCE(kvm_lapic_reg_read(apic, APIC_ICR2, 4, &high)))
+ return 1;
+
+ *data = (((u64)high) << 32) | low;
+
+ return 0;
+}
+
+static int kvm_lapic_msr_write(struct kvm_lapic *apic, u32 reg, u64 data)
+{
+ /* For 64-bit ICR writes, set ICR2 (dest) before ICR (command). */
+ if (reg == APIC_ICR)
+ kvm_lapic_reg_write(apic, APIC_ICR2, (u32)(data >> 32));
+ return kvm_lapic_reg_write(apic, reg, (u32)data);
+}
+
int kvm_x2apic_msr_write(struct kvm_vcpu *vcpu, u32 msr, u64 data)
{
struct kvm_lapic *apic = vcpu->arch.apic;
@@ -2798,16 +2822,13 @@ int kvm_x2apic_msr_write(struct kvm_vcpu *vcpu, u32 msr, u64 data)
if (reg == APIC_ICR2)
return 1;
- /* if this is ICR write vector before command */
- if (reg == APIC_ICR)
- kvm_lapic_reg_write(apic, APIC_ICR2, (u32)(data >> 32));
- return kvm_lapic_reg_write(apic, reg, (u32)data);
+ return kvm_lapic_msr_write(apic, reg, data);
}
int kvm_x2apic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data)
{
struct kvm_lapic *apic = vcpu->arch.apic;
- u32 reg = (msr - APIC_BASE_MSR) << 4, low, high = 0;
+ u32 reg = (msr - APIC_BASE_MSR) << 4;
if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(apic))
return 1;
@@ -2815,45 +2836,23 @@ int kvm_x2apic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data)
if (reg == APIC_DFR || reg == APIC_ICR2)
return 1;
- if (kvm_lapic_reg_read(apic, reg, 4, &low))
- return 1;
- if (reg == APIC_ICR)
- kvm_lapic_reg_read(apic, APIC_ICR2, 4, &high);
-
- *data = (((u64)high) << 32) | low;
-
- return 0;
+ return kvm_lapic_msr_read(apic, reg, data);
}
int kvm_hv_vapic_msr_write(struct kvm_vcpu *vcpu, u32 reg, u64 data)
{
- struct kvm_lapic *apic = vcpu->arch.apic;
-
if (!lapic_in_kernel(vcpu))
return 1;
- /* if this is ICR write vector before command */
- if (reg == APIC_ICR)
- kvm_lapic_reg_write(apic, APIC_ICR2, (u32)(data >> 32));
- return kvm_lapic_reg_write(apic, reg, (u32)data);
+ return kvm_lapic_msr_write(vcpu->arch.apic, reg, data);
}
int kvm_hv_vapic_msr_read(struct kvm_vcpu *vcpu, u32 reg, u64 *data)
{
- struct kvm_lapic *apic = vcpu->arch.apic;
- u32 low, high = 0;
-
if (!lapic_in_kernel(vcpu))
return 1;
- if (kvm_lapic_reg_read(apic, reg, 4, &low))
- return 1;
- if (reg == APIC_ICR)
- kvm_lapic_reg_read(apic, APIC_ICR2, 4, &high);
-
- *data = (((u64)high) << 32) | low;
-
- return 0;
+ return kvm_lapic_msr_read(vcpu->arch.apic, reg, data);
}
int kvm_lapic_set_pv_eoi(struct kvm_vcpu *vcpu, u64 data, unsigned long len)
--
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