linux-kernel - [PATCH v7 39/72] x86/sev-es: Setup early #VC handler

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Date:   Mon,  7 Sep 2020 15:15:40 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v7 39/72] x86/sev-es: Setup early #VC handler

From: Joerg Roedel <jroedel@...e.de>

Setup an early handler for #VC exceptions. There is no GHCB mapped
yet, so just re-use the vc_no_ghcb_handler. It can only handle CPUID
exit-codes, but that should be enough to get the kernel through
verify_cpu() and __startup_64() until it runs on virtual addresses.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/include/asm/sev-es.h |  3 +++
 arch/x86/kernel/head64.c      | 20 ++++++++++++++++++++
 arch/x86/kernel/head_64.S     | 27 +++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 6dc52440c4b4..7175d432ebfe 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -73,4 +73,7 @@ static inline u64 lower_bits(u64 val, unsigned int bits)
 	return (val & mask);
 }
 
+/* Early IDT entry points for #VC handler */
+extern void vc_no_ghcb(void);
+
 #endif
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 4282dac694c3..621b5e8aef4c 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -40,6 +40,7 @@
 #include <asm/desc.h>
 #include <asm/extable.h>
 #include <asm/trapnr.h>
+#include <asm/sev-es.h>
 
 /*
  * Manage page tables very early on.
@@ -540,10 +541,29 @@ static struct desc_ptr bringup_idt_descr = {
 	.address	= 0, /* Set at runtime */
 };
 
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+static void set_bringup_idt_handler(int n, void *handler)
+{
+	struct idt_data data;
+	gate_desc desc;
+
+	init_idt_data(&data, n, handler);
+	idt_init_desc(&desc, &data);
+	native_write_idt_entry(bringup_idt_table, n, &desc);
+}
+#endif
+
 /* This runs while still in the direct mapping */
 static void startup_64_load_idt(unsigned long physbase)
 {
 	struct desc_ptr *desc = fixup_pointer(&bringup_idt_descr, physbase);
+	void __maybe_unused *handler;
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+	/* VMM Communication Exception */
+	handler = fixup_pointer(vc_no_ghcb, physbase);
+	set_bringup_idt_handler(X86_TRAP_VC, handler);
+#endif
 
 	desc->address = (unsigned long)fixup_pointer(bringup_idt_table, physbase);
 	native_load_idt(desc);
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 3b40ec44a67d..2e5aa03b4321 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -348,6 +348,33 @@ SYM_CODE_START_LOCAL(early_idt_handler_common)
 	jmp restore_regs_and_return_to_kernel
 SYM_CODE_END(early_idt_handler_common)
 
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+/*
+ * VC Exception handler used during very early boot. The
+ * early_idt_handler_array can't be used because it returns via the
+ * paravirtualized INTERRUPT_RETURN and pv-ops don't work that early.
+ */
+SYM_CODE_START_NOALIGN(vc_no_ghcb)
+	UNWIND_HINT_IRET_REGS offset=8
+
+	/* Build pt_regs */
+	PUSH_AND_CLEAR_REGS
+
+	/* Call C handler */
+	movq    %rsp, %rdi
+	movq	ORIG_RAX(%rsp), %rsi
+	call    do_vc_no_ghcb
+
+	/* Unwind pt_regs */
+	POP_REGS
+
+	/* Remove Error Code */
+	addq    $8, %rsp
+
+	/* Pure iret required here - don't use INTERRUPT_RETURN */
+	iretq
+SYM_CODE_END(vc_no_ghcb)
+#endif
 
 #define SYM_DATA_START_PAGE_ALIGNED(name)			\
 	SYM_START(name, SYM_L_GLOBAL, .balign PAGE_SIZE)
-- 
2.28.0