[PATCH Part1 RFC v4 31/36] x86/sev: Provide support for SNP guest request NAEs

[Brijesh Singh]

Version 2 of GHCB specification provides SNP_GUEST_REQUEST and
SNP_EXT_GUEST_REQUEST NAE that can be used by the SNP guest to communicate
with the PSP.

While at it, add a snp_issue_guest_request() helper that can be used by
driver or other subsystem to issue the request to PSP.

See SEV-SNP and GHCB spec for more details.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/include/uapi/asm/svm.h |  4 +++
 arch/x86/kernel/sev.c           | 57 +++++++++++++++++++++++++++++++++
 include/linux/sev-guest.h       | 48 +++++++++++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100644 include/linux/sev-guest.h

diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
index 997918f0a89a..9aaf0ab386ef 100644
--- a/arch/x86/include/uapi/asm/svm.h
+++ b/arch/x86/include/uapi/asm/svm.h
@@ -109,6 +109,8 @@
 #define SVM_VMGEXIT_SET_AP_JUMP_TABLE		0
 #define SVM_VMGEXIT_GET_AP_JUMP_TABLE		1
 #define SVM_VMGEXIT_PSC				0x80000010
+#define SVM_VMGEXIT_GUEST_REQUEST		0x80000011
+#define SVM_VMGEXIT_EXT_GUEST_REQUEST		0x80000012
 #define SVM_VMGEXIT_AP_CREATION			0x80000013
 #define SVM_VMGEXIT_AP_CREATE_ON_INIT		0
 #define SVM_VMGEXIT_AP_CREATE			1
@@ -221,6 +223,8 @@
 	{ SVM_VMGEXIT_NMI_COMPLETE,	"vmgexit_nmi_complete" }, \
 	{ SVM_VMGEXIT_AP_HLT_LOOP,	"vmgexit_ap_hlt_loop" }, \
 	{ SVM_VMGEXIT_AP_JUMP_TABLE,	"vmgexit_ap_jump_table" }, \
+	{ SVM_VMGEXIT_GUEST_REQUEST,	"vmgexit_guest_request" }, \
+	{ SVM_VMGEXIT_EXT_GUEST_REQUEST,	"vmgexit_ext_guest_request" }, \
 	{ SVM_VMGEXIT_PSC,	"vmgexit_page_state_change" }, \
 	{ SVM_VMGEXIT_AP_CREATION,	"vmgexit_ap_creation" }, \
 	{ SVM_VMGEXIT_HYPERVISOR_FEATURES,	"vmgexit_hypervisor_feature" }, \
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 04ef5e79fa12..b85cab838372 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -21,6 +21,7 @@
 #include <linux/cpumask.h>
 #include <linux/log2.h>
 #include <linux/efi.h>
+#include <linux/sev-guest.h>
 
 #include <asm/cpu_entry_area.h>
 #include <asm/stacktrace.h>
@@ -2024,3 +2025,59 @@ bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
 	while (true)
 		halt();
 }
+
+int snp_issue_guest_request(int type, struct snp_guest_request_data *input, unsigned long *fw_err)
+{
+	struct ghcb_state state;
+	unsigned long id, flags;
+	struct ghcb *ghcb;
+	int ret;
+
+	if (!sev_feature_enabled(SEV_SNP))
+		return -ENODEV;
+
+
+	local_irq_save(flags);
+
+	ghcb = __sev_get_ghcb(&state);
+	if (!ghcb)
+		return -ENODEV;
+
+	vc_ghcb_invalidate(ghcb);
+
+	if (type == GUEST_REQUEST) {
+		id = SVM_VMGEXIT_GUEST_REQUEST;
+	} else if (type == EXT_GUEST_REQUEST) {
+		id = SVM_VMGEXIT_EXT_GUEST_REQUEST;
+		ghcb_set_rax(ghcb, input->data_gpa);
+		ghcb_set_rbx(ghcb, input->data_npages);
+	} else {
+		ret = -EINVAL;
+		goto e_put;
+	}
+
+
+	ret = sev_es_ghcb_hv_call(ghcb, NULL, id, input->req_gpa, input->resp_gpa);
+	if (ret)
+		goto e_put;
+
+	if (ghcb->save.sw_exit_info_2) {
+
+		/* Number of expected pages are returned in RBX */
+		if (id == EXT_GUEST_REQUEST)
+			input->data_npages = ghcb_get_rbx(ghcb);
+
+		if (fw_err)
+			*fw_err = ghcb->save.sw_exit_info_2;
+
+		ret = -EIO;
+		goto e_put;
+	}
+
+e_put:
+	__sev_put_ghcb(&state);
+	local_irq_restore(flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(snp_issue_guest_request);
diff --git a/include/linux/sev-guest.h b/include/linux/sev-guest.h
new file mode 100644
index 000000000000..24dd17507789
--- /dev/null
+++ b/include/linux/sev-guest.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * AMD Secure Encrypted Virtualization (SEV) guest driver interface
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ *
+ * Author: Brijesh Singh <brijesh.singh@xxxxxxx>
+ *
+ */
+
+#ifndef __LINUX_SEV_GUEST_H_
+#define __LINUX_SEV_GUEST_H_
+
+#include <linux/types.h>
+
+enum vmgexit_type {
+	GUEST_REQUEST,
+	EXT_GUEST_REQUEST,
+
+	GUEST_REQUEST_MAX
+};
+
+/*
+ * The error code when the data_npages is too small. The error code
+ * is defined in the GHCB specification.
+ */
+#define SNP_GUEST_REQ_INVALID_LEN	0x100000000ULL
+
+struct snp_guest_request_data {
+	unsigned long req_gpa;
+	unsigned long resp_gpa;
+	unsigned long data_gpa;
+	unsigned int data_npages;
+};
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+int snp_issue_guest_request(int vmgexit_type, struct snp_guest_request_data *input,
+			    unsigned long *fw_err);
+#else
+
+static inline int snp_issue_guest_request(int type, struct snp_guest_request_data *input,
+					  unsigned long *fw_err)
+{
+	return -ENODEV;
+}
+
+#endif /* CONFIG_AMD_MEM_ENCRYPT */
+#endif /* __LINUX_SEV_GUEST_H__ */
-- 
2.17.1