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Message-ID: <20250828110255.208779-1-Neeraj.Upadhyay@amd.com>
Date: Thu, 28 Aug 2025 16:32:40 +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>, <francescolavra.fl@...il.com>, <tiala@...rosoft.com>
Subject: [PATCH v10 03/18] x86/apic: Populate .read()/.write() callbacks of Secure AVIC driver
Add read() and write() APIC callback functions to read and write the
x2APIC registers directly from the guest APIC backing page of a vCPU.
The x2APIC registers are mapped at an offset within the guest APIC
backing page which is same as their x2APIC MMIO offset. Secure AVIC
adds new registers such as ALLOWED_IRRs (which are at 4-byte offset
within the IRR register offset range) and NMI_REQ to the APIC register
space.
When Secure AVIC is enabled, guest's RDMSR/WRMSR of the APIC registers
result in #VC exception (for non-accelerated register accesses) with
error code VMEXIT_AVIC_NOACCEL. The #VC exception handler can read/write
the x2APIC register in the guest APIC backing page to complete the
RDMSR/WRMSR. Since doing this would increase the latency of accessing
the x2APIC registers, instead of doing RDMSR/WRMSR based register
accesses and handling reads/writes in the #VC exception, directly
read/write the APIC registers from/to the guest APIC backing page of
the vCPU in read() and write() callbacks of the Secure AVIC APIC
driver.
Co-developed-by: Kishon Vijay Abraham I <kvijayab@....com>
Signed-off-by: Kishon Vijay Abraham I <kvijayab@....com>
Reviewed-by: Tianyu Lan <tiala@...rosoft.com>
Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
---
Changes since v9:
- Clean up the ALLOWED_IRR alignment condition check.
- Update comments describing the alignment of APIC_IRR and
ALLOWED_IRR.
- Commit log updates.
arch/x86/include/asm/apicdef.h | 2 +
arch/x86/kernel/apic/x2apic_savic.c | 122 +++++++++++++++++++++++++++-
2 files changed, 122 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/apicdef.h b/arch/x86/include/asm/apicdef.h
index 094106b6a538..be39a543fbe5 100644
--- a/arch/x86/include/asm/apicdef.h
+++ b/arch/x86/include/asm/apicdef.h
@@ -135,6 +135,8 @@
#define APIC_TDR_DIV_128 0xA
#define APIC_EFEAT 0x400
#define APIC_ECTRL 0x410
+#define APIC_SEOI 0x420
+#define APIC_IER 0x480
#define APIC_EILVTn(n) (0x500 + 0x10 * n)
#define APIC_EILVT_NR_AMD_K8 1 /* # of extended interrupts */
#define APIC_EILVT_NR_AMD_10H 4
diff --git a/arch/x86/kernel/apic/x2apic_savic.c b/arch/x86/kernel/apic/x2apic_savic.c
index 948d89497baa..5479605429c1 100644
--- a/arch/x86/kernel/apic/x2apic_savic.c
+++ b/arch/x86/kernel/apic/x2apic_savic.c
@@ -9,6 +9,7 @@
#include <linux/cc_platform.h>
#include <linux/percpu-defs.h>
+#include <linux/align.h>
#include <asm/apic.h>
#include <asm/sev.h>
@@ -26,6 +27,123 @@ static int savic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
return x2apic_enabled() && cc_platform_has(CC_ATTR_SNP_SECURE_AVIC);
}
+#define SAVIC_ALLOWED_IRR 0x204
+
+/*
+ * When Secure AVIC is enabled, RDMSR/WRMSR of the APIC registers
+ * result in #VC exception (for non-accelerated register accesses)
+ * with VMEXIT_AVIC_NOACCEL error code. The #VC exception handler
+ * can read/write the x2APIC register in the guest APIC backing page.
+ *
+ * Since doing this would increase the latency of accessing x2APIC
+ * registers, instead of doing RDMSR/WRMSR based accesses and
+ * handling the APIC register reads/writes in the #VC exception handler,
+ * the read() and write() callbacks directly read/write the APIC register
+ * from/to the vCPU's APIC backing page.
+ */
+static u32 savic_read(u32 reg)
+{
+ void *ap = this_cpu_ptr(savic_page);
+
+ switch (reg) {
+ case APIC_LVTT:
+ case APIC_TMICT:
+ case APIC_TMCCT:
+ case APIC_TDCR:
+ case APIC_ID:
+ case APIC_LVR:
+ case APIC_TASKPRI:
+ case APIC_ARBPRI:
+ case APIC_PROCPRI:
+ case APIC_LDR:
+ case APIC_SPIV:
+ case APIC_ESR:
+ case APIC_LVTTHMR:
+ case APIC_LVTPC:
+ case APIC_LVT0:
+ case APIC_LVT1:
+ case APIC_LVTERR:
+ case APIC_EFEAT:
+ case APIC_ECTRL:
+ case APIC_SEOI:
+ case APIC_IER:
+ case APIC_EILVTn(0) ... APIC_EILVTn(3):
+ return apic_get_reg(ap, reg);
+ case APIC_ICR:
+ return (u32)apic_get_reg64(ap, reg);
+ case APIC_ISR ... APIC_ISR + 0x70:
+ case APIC_TMR ... APIC_TMR + 0x70:
+ if (WARN_ONCE(!IS_ALIGNED(reg, 16),
+ "APIC register read offset 0x%x not aligned at 16 bytes", reg))
+ return 0;
+ return apic_get_reg(ap, reg);
+ /* IRR and ALLOWED_IRR offset range */
+ case APIC_IRR ... APIC_IRR + 0x74:
+ /*
+ * Valid APIC_IRR/SAVIC_ALLOWED_IRR registers are at 16 bytes strides from
+ * their respective base offset. APIC_IRRs are in the range
+ *
+ * (0x200, 0x210, ..., 0x270)
+ *
+ * while the SAVIC_ALLOWED_IRR range starts 4 bytes later, in the range
+ *
+ * (0x204, 0x214, ..., 0x274).
+ *
+ * Filter out everything else.
+ */
+ if (WARN_ONCE(!(IS_ALIGNED(reg, 16) ||
+ IS_ALIGNED(reg - 4, 16)),
+ "Misaligned APIC_IRR/ALLOWED_IRR APIC register read offset 0x%x", reg))
+ return 0;
+ return apic_get_reg(ap, reg);
+ default:
+ pr_err("Error reading unknown Secure AVIC reg offset 0x%x\n", reg);
+ return 0;
+ }
+}
+
+#define SAVIC_NMI_REQ 0x278
+
+static void savic_write(u32 reg, u32 data)
+{
+ void *ap = this_cpu_ptr(savic_page);
+
+ switch (reg) {
+ case APIC_LVTT:
+ case APIC_LVT0:
+ case APIC_LVT1:
+ case APIC_TMICT:
+ case APIC_TDCR:
+ case APIC_SELF_IPI:
+ case APIC_TASKPRI:
+ case APIC_EOI:
+ case APIC_SPIV:
+ case SAVIC_NMI_REQ:
+ case APIC_ESR:
+ case APIC_LVTTHMR:
+ case APIC_LVTPC:
+ case APIC_LVTERR:
+ case APIC_ECTRL:
+ case APIC_SEOI:
+ case APIC_IER:
+ case APIC_EILVTn(0) ... APIC_EILVTn(3):
+ apic_set_reg(ap, reg, data);
+ break;
+ case APIC_ICR:
+ apic_set_reg64(ap, reg, (u64)data);
+ break;
+ /* ALLOWED_IRR offsets are writable */
+ case SAVIC_ALLOWED_IRR ... SAVIC_ALLOWED_IRR + 0x70:
+ if (IS_ALIGNED(reg - 4, 16)) {
+ apic_set_reg(ap, reg, data);
+ break;
+ }
+ fallthrough;
+ default:
+ pr_err("Error writing unknown Secure AVIC reg offset 0x%x\n", reg);
+ }
+}
+
static void savic_setup(void)
{
void *ap = this_cpu_ptr(savic_page);
@@ -88,8 +206,8 @@ static struct apic apic_x2apic_savic __ro_after_init = {
.nmi_to_offline_cpu = true,
- .read = native_apic_msr_read,
- .write = native_apic_msr_write,
+ .read = savic_read,
+ .write = savic_write,
.eoi = native_apic_msr_eoi,
.icr_read = native_x2apic_icr_read,
.icr_write = native_x2apic_icr_write,
--
2.34.1
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