x86/boot/compressed/64: Add stage1 #VC handler

Add the first handler for #VC exceptions. At stage 1 there is no GHCB
yet because the kernel might still be running on the EFI page table.

The stage 1 handler is limited to the MSR-based protocol to talk to the
hypervisor and can only support CPUID exit-codes, but that is enough to
get to stage 2.

 [ bp: Zap superfluous newlines after rd/wrmsr instruction mnemonics. ]

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-20-joro@8bytes.org

1 files changed, 66 insertions, 0 deletions

diff --git a/arch/x86/kernel/sev-es-shared.c b/arch/x86/kernel/sev-es-shared.c
new file mode 100644
index 000000000000..0bea32341afa
--- /dev/null
+++ b/arch/x86/kernel/sev-es-shared.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * AMD Encrypted Register State Support
+ *
+ * Author: Joerg Roedel <jroedel@suse.de>
+ *
+ * This file is not compiled stand-alone. It contains code shared
+ * between the pre-decompression boot code and the running Linux kernel
+ * and is included directly into both code-bases.
+ */
+
+/*
+ * Boot VC Handler - This is the first VC handler during boot, there is no GHCB
+ * page yet, so it only supports the MSR based communication with the
+ * hypervisor and only the CPUID exit-code.
+ */
+void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
+{
+	unsigned int fn = lower_bits(regs->ax, 32);
+	unsigned long val;
+
+	/* Only CPUID is supported via MSR protocol */
+	if (exit_code != SVM_EXIT_CPUID)
+		goto fail;
+
+	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EAX));
+	VMGEXIT();
+	val = sev_es_rd_ghcb_msr();
+	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+		goto fail;
+	regs->ax = val >> 32;
+
+	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EBX));
+	VMGEXIT();
+	val = sev_es_rd_ghcb_msr();
+	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+		goto fail;
+	regs->bx = val >> 32;
+
+	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_ECX));
+	VMGEXIT();
+	val = sev_es_rd_ghcb_msr();
+	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+		goto fail;
+	regs->cx = val >> 32;
+
+	sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EDX));
+	VMGEXIT();
+	val = sev_es_rd_ghcb_msr();
+	if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+		goto fail;
+	regs->dx = val >> 32;
+
+	/* Skip over the CPUID two-byte opcode */
+	regs->ip += 2;
+
+	return;
+
+fail:
+	sev_es_wr_ghcb_msr(GHCB_SEV_TERMINATE);
+	VMGEXIT();
+
+	/* Shouldn't get here - if we do halt the machine */
+	while (true)
+		asm volatile("hlt\n");
+}