linux-kernel - [RFC v2 07/17] x86/apic: Support LAPIC timer for Secure AVIC

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Message-ID: <20250226090525.231882-8-Neeraj.Upadhyay@amd.com>
Date: Wed, 26 Feb 2025 14:35:15 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: <linux-kernel@...r.kernel.org>
CC: <bp@...en8.de>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<dave.hansen@...ux.intel.com>, <Thomas.Lendacky@....com>, <nikunj@....com>,
	<Santosh.Shukla@....com>, <Vasant.Hegde@....com>,
	<Suravee.Suthikulpanit@....com>, <David.Kaplan@....com>, <x86@...nel.org>,
	<hpa@...or.com>, <peterz@...radead.org>, <seanjc@...gle.com>,
	<pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<kirill.shutemov@...ux.intel.com>, <huibo.wang@....com>, <naveen.rao@....com>
Subject: [RFC v2 07/17] x86/apic: Support LAPIC timer for Secure AVIC

From: Kishon Vijay Abraham I <kvijayab@....com>

Secure AVIC requires LAPIC timer to be emulated by hypervisor. KVM
already supports emulating LAPIC timer using hrtimers. In order
to emulate LAPIC timer, APIC_LVTT, APIC_TMICT and APIC_TDCR register
values need to be propagated to the hypervisor for arming the timer.
APIC_TMCCT register value has to be read from the hypervisor, which
is required for calibrating the APIC timer. So, read/write all APIC
timer registers from/to the hypervisor.

In addition, configure APIC_ALLOWED_IRR for the hypervisor to inject
timer interrupt using LOCAL_TIMER_VECTOR.

Signed-off-by: Kishon Vijay Abraham I <kvijayab@....com>
Co-developed-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
---
Changes since v1:

 - Move savic_ghcb_msr_read() definition here.
 - Call update_vector() callback only when it is initialized.

 arch/x86/coco/sev/core.c            | 27 +++++++++++++++++++++++++++
 arch/x86/include/asm/sev.h          |  2 ++
 arch/x86/kernel/apic/apic.c         |  4 ++++
 arch/x86/kernel/apic/x2apic_savic.c |  7 +++++--
 4 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 4291cdeb5895..e4c20023e554 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1505,6 +1505,33 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 	return __vc_handle_msr(ghcb, ctxt, ctxt->insn.opcode.bytes[1] == 0x30);
 }
 
+u64 savic_ghcb_msr_read(u32 reg)
+{
+	u64 msr = APIC_BASE_MSR + (reg >> 4);
+	struct pt_regs regs = { .cx = msr };
+	struct es_em_ctxt ctxt = { .regs = &regs };
+	struct ghcb_state state;
+	unsigned long flags;
+	enum es_result ret;
+	struct ghcb *ghcb;
+
+	local_irq_save(flags);
+	ghcb = __sev_get_ghcb(&state);
+	vc_ghcb_invalidate(ghcb);
+
+	ret = __vc_handle_msr(ghcb, &ctxt, false);
+	if (ret != ES_OK) {
+		pr_err("Secure AVIC msr (0x%llx) read returned error (%d)\n", msr, ret);
+		/* MSR read failures are treated as fatal errors */
+		snp_abort();
+	}
+
+	__sev_put_ghcb(&state);
+	local_irq_restore(flags);
+
+	return regs.ax | regs.dx << 32;
+}
+
 void savic_ghcb_msr_write(u32 reg, u64 value)
 {
 	u64 msr = APIC_BASE_MSR + (reg >> 4);
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 1beeb0daf9e6..043fe8115ec7 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -484,6 +484,7 @@ int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req
 void __init snp_secure_tsc_prepare(void);
 void __init snp_secure_tsc_init(void);
 enum es_result savic_register_gpa(u64 apic_id, u64 gpa);
+u64 savic_ghcb_msr_read(u32 reg);
 void savic_ghcb_msr_write(u32 reg, u64 value);
 
 #else	/* !CONFIG_AMD_MEM_ENCRYPT */
@@ -530,6 +531,7 @@ static inline void __init snp_secure_tsc_prepare(void) { }
 static inline void __init snp_secure_tsc_init(void) { }
 static inline enum es_result savic_register_gpa(u64 apic_id,
 						u64 gpa) { return ES_UNSUPPORTED; }
+static inline u64 savic_ghcb_msr_read(u32 reg) { return 0; }
 static void savic_ghcb_msr_write(u32 reg, u64 value) { }
 
 #endif	/* CONFIG_AMD_MEM_ENCRYPT */
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 1c0b5f14435e..23a566a82084 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -591,6 +591,10 @@ static void setup_APIC_timer(void)
 						0xF, ~0UL);
 	} else
 		clockevents_register_device(levt);
+
+	if (apic->update_vector)
+		apic->update_vector(smp_processor_id(), LOCAL_TIMER_VECTOR,
+				    true);
 }
 
 /*
diff --git a/arch/x86/kernel/apic/x2apic_savic.c b/arch/x86/kernel/apic/x2apic_savic.c
index 7e3843154997..af46e1b57017 100644
--- a/arch/x86/kernel/apic/x2apic_savic.c
+++ b/arch/x86/kernel/apic/x2apic_savic.c
@@ -71,6 +71,7 @@ static u32 x2apic_savic_read(u32 reg)
 	case APIC_TMICT:
 	case APIC_TMCCT:
 	case APIC_TDCR:
+		return savic_ghcb_msr_read(reg);
 	case APIC_ID:
 	case APIC_LVR:
 	case APIC_TASKPRI:
@@ -123,10 +124,12 @@ static void x2apic_savic_write(u32 reg, u32 data)
 
 	switch (reg) {
 	case APIC_LVTT:
-	case APIC_LVT0:
-	case APIC_LVT1:
 	case APIC_TMICT:
 	case APIC_TDCR:
+		savic_ghcb_msr_write(reg, data);
+		break;
+	case APIC_LVT0:
+	case APIC_LVT1:
 	case APIC_TASKPRI:
 	case APIC_EOI:
 	case APIC_SPIV:
-- 
2.34.1