[RFC Part1 PATCH 08/13] x86/sev-es: register GHCB memory when SEV-SNP is active

Brijesh Singh
2021-03-24T16:45:29Z

The SEV-SNP guest is required to perform GHCB GPA registration. This is
because the hypervisor may prefer that a guest use a consistent and/or
specific GPA for the GHCB associated with a vCPU. For more information,
see the GHCB specification section 2.5.2.

During the boot, init_ghcb() allocates a per-cpu GHCB page. On very first
VC exception, the exception handler switch to using the per-cpu GHCB page
allocated during the init_ghcb(). The GHCB page must be registered in
the current vcpu context.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/kernel/Makefile | 3 ++
arch/x86/kernel/sev-es.c | 19 +++++++++++++
arch/x86/kernel/sev-snp.c | 58 +++++++++++++++++++++++++++++++++++++++
3 files changed, 80 insertions(+)
create mode 100644 arch/x86/kernel/sev-snp.c

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 5eeb808eb024..2fb24c49d2e3 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -21,6 +21,7 @@ CFLAGS_REMOVE_ftrace.o = -pg
CFLAGS_REMOVE_early_printk.o = -pg
CFLAGS_REMOVE_head64.o = -pg
CFLAGS_REMOVE_sev-es.o = -pg
+CFLAGS_REMOVE_sev-snp.o = -pg
endif

KASAN_SANITIZE_head$(BITS).o := n
@@ -29,6 +30,7 @@ KASAN_SANITIZE_dumpstack_$(BITS).o := n
KASAN_SANITIZE_stacktrace.o := n
KASAN_SANITIZE_paravirt.o := n
KASAN_SANITIZE_sev-es.o := n
+KASAN_SANITIZE_sev-snp.o := n

# With some compiler versions the generated code results in boot hangs, caused
# by several compilation units. To be safe, disable all instrumentation.
@@ -151,6 +153,7 @@ obj-$(CONFIG_UNWINDER_FRAME_POINTER) += unwind_frame.o
obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o

obj-$(CONFIG_AMD_MEM_ENCRYPT) += sev-es.o
+obj-$(CONFIG_AMD_MEM_ENCRYPT) += sev-snp.o
###
# 64 bit specific files
ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 0bd1a0fc587e..004bf1102dc1 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -23,6 +23,7 @@
#include <asm/cpu_entry_area.h>
#include <asm/stacktrace.h>
#include <asm/sev-es.h>
+#include <asm/sev-snp.h>
#include <asm/insn-eval.h>
#include <asm/fpu/internal.h>
#include <asm/processor.h>
@@ -88,6 +89,13 @@ struct sev_es_runtime_data {
* is currently unsupported in SEV-ES guests.
*/
unsigned long dr7;
+
+ /*
+ * SEV-SNP requires that the GHCB must be registered before using it.
+ * The flag below will indicate whether the GHCB is registered, if its
+ * not registered then sev_es_get_ghcb() will perform the registration.
+ */
+ bool ghcb_registered;
};

struct ghcb_state {
@@ -196,6 +204,12 @@ static __always_inline struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
data->ghcb_active = true;
}

+ /* SEV-SNP guest requires that GHCB must be registered before using it. */
+ if (sev_snp_active() && !data->ghcb_registered) {
+ sev_snp_register_ghcb(__pa(ghcb));
+ data->ghcb_registered = true;
+ }
+
return ghcb;
}

@@ -569,6 +583,10 @@ static bool __init sev_es_setup_ghcb(void)
/* Alright - Make the boot-ghcb public */
boot_ghcb = &boot_ghcb_page;

+ /* SEV-SNP guest requires that GHCB GPA must be registered */
+ if (sev_snp_active())
+ sev_snp_register_ghcb(__pa(&boot_ghcb_page));
+
return true;
}

@@ -658,6 +676,7 @@ static void __init init_ghcb(int cpu)

data->ghcb_active = false;
data->backup_ghcb_active = false;
+ data->ghcb_registered = false;
}

void __init sev_es_init_vc_handling(void)
diff --git a/arch/x86/kernel/sev-snp.c b/arch/x86/kernel/sev-snp.c
new file mode 100644
index 000000000000..d32225c2b653
--- /dev/null
+++ b/arch/x86/kernel/sev-snp.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * AMD Memory Encryption Support
+ *
+ * Copyright (C) 2021 Advanced Micro Devices
+ *
+ * Author: Brijesh Singh <brijesh.singh@amd.com>
+ */
+
+#define pr_fmt(fmt) "SEV-SNP: " fmt
+
+#include <linux/mem_encrypt.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+
+#include <asm/sev-es.h>
+#include <asm/sev-snp.h>
+
+static inline u64 sev_es_rd_ghcb_msr(void)
+{
+ return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
+}
+
+static inline void sev_es_wr_ghcb_msr(u64 val)
+{
+ u32 low, high;
+
+ low = (u32)(val);
+ high = (u32)(val >> 32);
+
+ native_wrmsr(MSR_AMD64_SEV_ES_GHCB, low, high);
+}
+
+/* Provides sev_es_terminate() */
+#include "sev-common-shared.c"
+
+void sev_snp_register_ghcb(unsigned long paddr)
+{
+ u64 pfn = paddr >> PAGE_SHIFT;
+ u64 old, val;
+
+ /* save the old GHCB MSR */
+ old = sev_es_rd_ghcb_msr();
+
+ /* Issue VMGEXIT */
+ sev_es_wr_ghcb_msr(GHCB_REGISTER_GPA_REQ_VAL(pfn));
+ VMGEXIT();
+
+ val = sev_es_rd_ghcb_msr();
+
+ /* If the response GPA is not ours then abort the guest */
+ if ((GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_REGISTER_GPA_RESP) ||
+ (GHCB_REGISTER_GPA_RESP_VAL(val) != pfn))
+ sev_es_terminate(GHCB_SEV_ES_REASON_GENERAL_REQUEST);
+
+ /* Restore the GHCB MSR value */
+ sev_es_wr_ghcb_msr(old);
+}
--
2.17.1