Drivers: hv: Introduce mshv_vtl driver

Provide an interface for Virtual Machine Monitor like OpenVMM and its
use as OpenHCL paravisor to control VTL0 (Virtual trust Level).
Expose devices and support IOCTLs for features like VTL creation,
VTL0 memory management, context switch, making hypercalls,
mapping VTL0 address space to VTL2 userspace, getting new VMBus
messages and channel events in VTL2 etc.

Co-developed-by: Roman Kisel <romank@linux.microsoft.com>
Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Co-developed-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

5 files changed, 226 insertions, 1 deletions

diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
index 6f5d97cddd80..56292102af62 100644
--- a/arch/x86/hyperv/Makefile
+++ b/arch/x86/hyperv/Makefile
@@ -1,7 +1,12 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y			:= hv_init.o mmu.o nested.o irqdomain.o ivm.o
 obj-$(CONFIG_X86_64)	+= hv_apic.o
-obj-$(CONFIG_HYPERV_VTL_MODE)	+= hv_vtl.o
+obj-$(CONFIG_HYPERV_VTL_MODE)	+= hv_vtl.o mshv_vtl_asm.o
+
+$(obj)/mshv_vtl_asm.o: $(obj)/mshv-asm-offsets.h
+
+$(obj)/mshv-asm-offsets.h: $(obj)/mshv-asm-offsets.s FORCE
+	$(call filechk,offsets,__MSHV_ASM_OFFSETS_H__)
 
 ifdef CONFIG_X86_64
 obj-$(CONFIG_PARAVIRT_SPINLOCKS)	+= hv_spinlock.o
@@ -12,3 +17,6 @@ obj-$(CONFIG_PARAVIRT_SPINLOCKS)	+= hv_spinlock.o
   obj-$(CONFIG_CRASH_DUMP)      += hv_crash.o hv_trampoline.o
  endif
 endif
+
+targets += mshv-asm-offsets.s
+clean-files += mshv-asm-offsets.h
diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 042e8712d8de..c0edaed0efb3 100644
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -9,12 +9,17 @@
 #include <asm/apic.h>
 #include <asm/boot.h>
 #include <asm/desc.h>
+#include <asm/fpu/api.h>
+#include <asm/fpu/types.h>
 #include <asm/i8259.h>
 #include <asm/mshyperv.h>
 #include <asm/msr.h>
 #include <asm/realmode.h>
 #include <asm/reboot.h>
+#include <asm/smap.h>
+#include <linux/export.h>
 #include <../kernel/smpboot.h>
+#include "../../kernel/fpu/legacy.h"
 
 extern struct boot_params boot_params;
 static struct real_mode_header hv_vtl_real_mode_header;
@@ -249,3 +254,28 @@ int __init hv_vtl_early_init(void)
 
 	return 0;
 }
+
+DEFINE_STATIC_CALL_NULL(__mshv_vtl_return_hypercall, void (*)(void));
+
+void mshv_vtl_return_call_init(u64 vtl_return_offset)
+{
+	static_call_update(__mshv_vtl_return_hypercall,
+			   (void *)((u8 *)hv_hypercall_pg + vtl_return_offset));
+}
+EXPORT_SYMBOL(mshv_vtl_return_call_init);
+
+void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
+{
+	struct hv_vp_assist_page *hvp;
+
+	hvp = hv_vp_assist_page[smp_processor_id()];
+	hvp->vtl_ret_x64rax = vtl0->rax;
+	hvp->vtl_ret_x64rcx = vtl0->rcx;
+
+	kernel_fpu_begin_mask(0);
+	fxrstor(&vtl0->fx_state);
+	__mshv_vtl_return_call(vtl0);
+	fxsave(&vtl0->fx_state);
+	kernel_fpu_end();
+}
+EXPORT_SYMBOL(mshv_vtl_return_call);
diff --git a/arch/x86/hyperv/mshv-asm-offsets.c b/arch/x86/hyperv/mshv-asm-offsets.c
new file mode 100644
index 000000000000..882c1db6df16
--- /dev/null
+++ b/arch/x86/hyperv/mshv-asm-offsets.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generate definitions needed by assembly language modules.
+ * This code generates raw asm output which is post-processed to extract
+ * and format the required data.
+ *
+ * Copyright (c) 2025, Microsoft Corporation.
+ *
+ * Author:
+ *   Naman Jain <namjain@microsoft.com>
+ */
+#define COMPILE_OFFSETS
+
+#include <linux/kbuild.h>
+#include <asm/mshyperv.h>
+
+static void __used common(void)
+{
+	if (IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) {
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rax, mshv_vtl_cpu_context, rax);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rcx, mshv_vtl_cpu_context, rcx);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rdx, mshv_vtl_cpu_context, rdx);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rbx, mshv_vtl_cpu_context, rbx);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rbp, mshv_vtl_cpu_context, rbp);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rsi, mshv_vtl_cpu_context, rsi);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_rdi, mshv_vtl_cpu_context, rdi);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r8,  mshv_vtl_cpu_context, r8);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r9,  mshv_vtl_cpu_context, r9);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r10, mshv_vtl_cpu_context, r10);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r11, mshv_vtl_cpu_context, r11);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r12, mshv_vtl_cpu_context, r12);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r13, mshv_vtl_cpu_context, r13);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r14, mshv_vtl_cpu_context, r14);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_r15, mshv_vtl_cpu_context, r15);
+		OFFSET(MSHV_VTL_CPU_CONTEXT_cr2, mshv_vtl_cpu_context, cr2);
+	}
+}
diff --git a/arch/x86/hyperv/mshv_vtl_asm.S b/arch/x86/hyperv/mshv_vtl_asm.S
new file mode 100644
index 000000000000..f595eefad9ab
--- /dev/null
+++ b/arch/x86/hyperv/mshv_vtl_asm.S
@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Assembly level code for mshv_vtl VTL transition
+ *
+ * Copyright (c) 2025, Microsoft Corporation.
+ *
+ * Author:
+ *   Naman Jain <namjain@microsoft.com>
+ */
+
+#include <linux/linkage.h>
+#include <linux/static_call_types.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/frame.h>
+#include "mshv-asm-offsets.h"
+
+	.text
+	.section .noinstr.text, "ax"
+/*
+ * void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
+ *
+ * This function is used to context switch between different Virtual Trust Levels.
+ * It is marked as 'noinstr' to prevent against instrumentation and debugging facilities.
+ * NMIs aren't a problem because the NMI handler saves/restores CR2 specifically to guard
+ * against #PFs in NMI context clobbering the guest state.
+ */
+SYM_FUNC_START(__mshv_vtl_return_call)
+	/* Push callee save registers */
+	pushq %rbp
+	mov %rsp, %rbp
+	pushq %r12
+	pushq %r13
+	pushq %r14
+	pushq %r15
+	pushq %rbx
+
+	/* register switch to VTL0 clobbers all registers except rax/rcx */
+	mov %_ASM_ARG1, %rax
+
+	/* grab rbx/rbp/rsi/rdi/r8-r15 */
+	mov MSHV_VTL_CPU_CONTEXT_rbx(%rax), %rbx
+	mov MSHV_VTL_CPU_CONTEXT_rbp(%rax), %rbp
+	mov MSHV_VTL_CPU_CONTEXT_rsi(%rax), %rsi
+	mov MSHV_VTL_CPU_CONTEXT_rdi(%rax), %rdi
+	mov MSHV_VTL_CPU_CONTEXT_r8(%rax), %r8
+	mov MSHV_VTL_CPU_CONTEXT_r9(%rax), %r9
+	mov MSHV_VTL_CPU_CONTEXT_r10(%rax), %r10
+	mov MSHV_VTL_CPU_CONTEXT_r11(%rax), %r11
+	mov MSHV_VTL_CPU_CONTEXT_r12(%rax), %r12
+	mov MSHV_VTL_CPU_CONTEXT_r13(%rax), %r13
+	mov MSHV_VTL_CPU_CONTEXT_r14(%rax), %r14
+	mov MSHV_VTL_CPU_CONTEXT_r15(%rax), %r15
+
+	mov MSHV_VTL_CPU_CONTEXT_cr2(%rax), %rdx
+	mov %rdx, %cr2
+	mov MSHV_VTL_CPU_CONTEXT_rdx(%rax), %rdx
+
+	/* stash host registers on stack */
+	pushq %rax
+	pushq %rcx
+
+	xor %ecx, %ecx
+
+	/* make a hypercall to switch VTL */
+	call STATIC_CALL_TRAMP_STR(__mshv_vtl_return_hypercall)
+
+	/* stash guest registers on stack, restore saved host copies */
+	pushq %rax
+	pushq %rcx
+	mov 16(%rsp), %rcx
+	mov 24(%rsp), %rax
+
+	mov %rdx, MSHV_VTL_CPU_CONTEXT_rdx(%rax)
+	mov %cr2, %rdx
+	mov %rdx, MSHV_VTL_CPU_CONTEXT_cr2(%rax)
+	pop MSHV_VTL_CPU_CONTEXT_rcx(%rax)
+	pop MSHV_VTL_CPU_CONTEXT_rax(%rax)
+	add $16, %rsp
+
+	/* save rbx/rbp/rsi/rdi/r8-r15 */
+	mov %rbx, MSHV_VTL_CPU_CONTEXT_rbx(%rax)
+	mov %rbp, MSHV_VTL_CPU_CONTEXT_rbp(%rax)
+	mov %rsi, MSHV_VTL_CPU_CONTEXT_rsi(%rax)
+	mov %rdi, MSHV_VTL_CPU_CONTEXT_rdi(%rax)
+	mov %r8,  MSHV_VTL_CPU_CONTEXT_r8(%rax)
+	mov %r9,  MSHV_VTL_CPU_CONTEXT_r9(%rax)
+	mov %r10, MSHV_VTL_CPU_CONTEXT_r10(%rax)
+	mov %r11, MSHV_VTL_CPU_CONTEXT_r11(%rax)
+	mov %r12, MSHV_VTL_CPU_CONTEXT_r12(%rax)
+	mov %r13, MSHV_VTL_CPU_CONTEXT_r13(%rax)
+	mov %r14, MSHV_VTL_CPU_CONTEXT_r14(%rax)
+	mov %r15, MSHV_VTL_CPU_CONTEXT_r15(%rax)
+
+	/* pop callee-save registers r12-r15, rbx */
+	pop %rbx
+	pop %r15
+	pop %r14
+	pop %r13
+	pop %r12
+
+	pop %rbp
+	RET
+SYM_FUNC_END(__mshv_vtl_return_call)
+/*
+ * Make sure that static_call_key symbol: __SCK____mshv_vtl_return_hypercall is accessible here.
+ * Below code is inspired from __ADDRESSABLE(sym) macro. Symbol name is kept simple, to avoid
+ * naming it something like "__UNIQUE_ID_addressable___SCK____mshv_vtl_return_hypercall_662.0"
+ * which would otherwise have been generated by the macro.
+ */
+	.section	.discard.addressable,"aw"
+	.align 8
+	.type	mshv_vtl_return_sym, @object
+	.size	mshv_vtl_return_sym, 8
+mshv_vtl_return_sym:
+	.quad	__SCK____mshv_vtl_return_hypercall
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 1342d55c2545..10037125099a 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -11,6 +11,7 @@
 #include <asm/paravirt.h>
 #include <asm/msr.h>
 #include <hyperv/hvhdk.h>
+#include <asm/fpu/types.h>
 
 /*
  * Hyper-V always provides a single IO-APIC at this MMIO address.
@@ -269,13 +270,46 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg) { return 0; }
 static inline int hv_apicid_to_vp_index(u32 apic_id) { return -EINVAL; }
 #endif /* CONFIG_HYPERV */
 
+struct mshv_vtl_cpu_context {
+	union {
+		struct {
+			u64 rax;
+			u64 rcx;
+			u64 rdx;
+			u64 rbx;
+			u64 cr2;
+			u64 rbp;
+			u64 rsi;
+			u64 rdi;
+			u64 r8;
+			u64 r9;
+			u64 r10;
+			u64 r11;
+			u64 r12;
+			u64 r13;
+			u64 r14;
+			u64 r15;
+		};
+		u64 gp_regs[16];
+	};
+
+	struct fxregs_state fx_state;
+};
 
 #ifdef CONFIG_HYPERV_VTL_MODE
 void __init hv_vtl_init_platform(void);
 int __init hv_vtl_early_init(void);
+void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
+void mshv_vtl_return_call_init(u64 vtl_return_offset);
+void mshv_vtl_return_hypercall(void);
+void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0);
 #else
 static inline void __init hv_vtl_init_platform(void) {}
 static inline int __init hv_vtl_early_init(void) { return 0; }
+static inline void mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
+static inline void mshv_vtl_return_call_init(u64 vtl_return_offset) {}
+static inline void mshv_vtl_return_hypercall(void) {}
+static inline void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0) {}
 #endif
 
 #include <asm-generic/mshyperv.h>