[PATCH v4 04/18] x86/apic: Populate .read()/.write() callbacks of Secure AVIC driver

[Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>]

Add read() and write() APIC callback functions to read and write 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 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
x2APIC registers, instead of doing rdmsr/wrmsr based reg accesses
and handling reads/writes in VC exception, directly read/write 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@amd.com>
Signed-off-by: Kishon Vijay Abraham I <kvijayab@amd.com>
Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
---
Changes since v3:

 - Removed "x2apic_" from savic's apic cbs func names.

 arch/x86/include/asm/apicdef.h      |   2 +
 arch/x86/kernel/apic/x2apic_savic.c | 116 +++++++++++++++++++++++++++-
 2 files changed, 116 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 0a2cb1c03d08..4761afc7527d 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>
@@ -32,6 +33,117 @@ 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);
 }
 
+static __always_inline u32 get_reg(unsigned int offset)
+{
+	return READ_ONCE(this_cpu_ptr(apic_page)->regs[offset >> 2]);
+}
+
+static __always_inline void set_reg(unsigned int offset, u32 val)
+{
+	WRITE_ONCE(this_cpu_ptr(apic_page)->regs[offset >> 2], val);
+}
+
+#define SAVIC_ALLOWED_IRR	0x204
+
+static u32 savic_read(u32 reg)
+{
+	/*
+	 * When Secure AVIC is enabled, rdmsr/wrmsr of 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 apic register reads/writes in VC exception, the read()
+	 * and write() callbacks directly read/write APIC register from/to
+	 * the vCPU APIC backing 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_ICR:
+	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 get_reg(reg);
+	case APIC_ISR ... APIC_ISR + 0x70:
+	case APIC_TMR ... APIC_TMR + 0x70:
+		if (WARN_ONCE(!IS_ALIGNED(reg, 16),
+			      "APIC reg read offset 0x%x not aligned at 16 bytes", reg))
+			return 0;
+		return get_reg(reg);
+	/* IRR and ALLOWED_IRR offset range */
+	case APIC_IRR ... APIC_IRR + 0x74:
+		/*
+		 * Either aligned at 16 bytes for valid IRR reg offset or a
+		 * valid Secure AVIC ALLOWED_IRR offset.
+		 */
+		if (WARN_ONCE(!(IS_ALIGNED(reg, 16) ||
+				IS_ALIGNED(reg - SAVIC_ALLOWED_IRR, 16)),
+			      "Misaligned IRR/ALLOWED_IRR APIC reg read offset 0x%x", reg))
+			return 0;
+		return get_reg(reg);
+	default:
+		pr_err("Permission denied: read of Secure AVIC reg offset 0x%x\n", reg);
+		return 0;
+	}
+}
+
+#define SAVIC_NMI_REQ		0x278
+
+static void savic_write(u32 reg, u32 data)
+{
+	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_ICR:
+	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):
+		set_reg(reg, data);
+		break;
+	/* ALLOWED_IRR offsets are writable */
+	case SAVIC_ALLOWED_IRR ... SAVIC_ALLOWED_IRR + 0x70:
+		if (IS_ALIGNED(reg - SAVIC_ALLOWED_IRR, 16)) {
+			set_reg(reg, data);
+			break;
+		}
+		fallthrough;
+	default:
+		pr_err("Permission denied: write to Secure AVIC reg offset 0x%x\n", reg);
+	}
+}
+
 static void savic_setup(void)
 {
 	void *backing_page;
@@ -95,8 +207,8 @@ 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