[PATCH 70/70] x86/sev-es: Add NMI state tracking

Joerg Roedel
2020-03-19T09:15:31Z

From: Joerg Roedel <jroedel@suse.de>

Keep NMI state in SEV-ES code so the kernel can re-enable NMIs for the
vCPU when it reaches IRET.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/entry/entry_64.S | 48 +++++++++++++++++++++++++++++++++
arch/x86/include/asm/sev-es.h | 27 +++++++++++++++++++
arch/x86/include/uapi/asm/svm.h | 1 +
arch/x86/kernel/nmi.c | 8 ++++++
arch/x86/kernel/sev-es.c | 31 ++++++++++++++++++++-
5 files changed, 114 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 729876d368c5..355470b36896 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -38,6 +38,7 @@
#include <asm/export.h>
#include <asm/frame.h>
#include <asm/nospec-branch.h>
+#include <asm/sev-es.h>
#include <linux/err.h>

#include "calling.h"
@@ -629,6 +630,13 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
ud2
1:
#endif
+
+ /*
+ * This code path is used by the NMI handler, so check if NMIs
+ * need to be re-enabled when running as an SEV-ES guest.
+ */
+ SEV_ES_IRET_CHECK
+
POP_REGS pop_rdi=0

/*
@@ -1474,6 +1482,8 @@ SYM_CODE_START(nmi)
movq $-1, %rsi
call do_nmi

+ SEV_ES_NMI_COMPLETE
+
/*
* Return back to user mode. We must *not* do the normal exit
* work, because we don't want to enable interrupts.
@@ -1599,6 +1609,7 @@ nested_nmi_out:
popq %rdx

/* We are returning to kernel mode, so this cannot result in a fault. */
+ SEV_ES_NMI_COMPLETE
iretq

first_nmi:
@@ -1687,6 +1698,12 @@ end_repeat_nmi:
movq $-1, %rsi
call do_nmi

+ /*
+ * When running as an SEV-ES guest, jump to the SEV-ES NMI IRET
+ * path.
+ */
+ SEV_ES_NMI_COMPLETE
+
/* Always restore stashed CR3 value (see paranoid_entry) */
RESTORE_CR3 scratch_reg=%r15 save_reg=%r14

@@ -1715,6 +1732,9 @@ nmi_restore:
std
movq $0, 5*8(%rsp) /* clear "NMI executing" */

+nmi_return:
+ UNWIND_HINT_IRET_REGS
+
/*
* iretq reads the "iret" frame and exits the NMI stack in a
* single instruction. We are returning to kernel mode, so this
@@ -1724,6 +1744,34 @@ nmi_restore:
iretq
SYM_CODE_END(nmi)

+#ifdef CONFIG_AMD_MEM_ENCRYPT
+SYM_CODE_START(sev_es_iret_user)
+ UNWIND_HINT_IRET_REGS offset=8
+ /*
+ * The kernel jumps here directly from
+ * swapgs_restore_regs_and_return_to_usermode. %rsp points already to
+ * trampoline stack, but %cr3 is still from kernel. User-regs are live
+ * except %rdi. Switch to user CR3, restore user %rdi and user gs_base
+ * and single-step over IRET
+ */
+ SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
+ popq %rdi
+ SWAPGS
+ /*
+ * Enable single-stepping and execute IRET. When IRET is
+ * finished the resulting #DB exception will cause a #VC
+ * exception to be raised. The #VC exception handler will send a
+ * NMI-complete message to the hypervisor to re-open the NMI
+ * window.
+ */
+sev_es_iret_kernel:
+ pushf
+ btsq $X86_EFLAGS_TF_BIT, (%rsp)
+ popf
+ iretq
+SYM_CODE_END(sev_es_iret_user)
+#endif
+
#ifndef CONFIG_IA32_EMULATION
/*
* This handles SYSCALL from 32-bit code. There is no way to program
diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 63acf50e6280..d866adb3e6d4 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -8,6 +8,8 @@
#ifndef __ASM_ENCRYPTED_STATE_H
#define __ASM_ENCRYPTED_STATE_H

+#ifndef __ASSEMBLY__
+
#include <linux/types.h>
#include <asm/insn.h>

@@ -82,11 +84,36 @@ struct real_mode_header;

#ifdef CONFIG_AMD_MEM_ENCRYPT
int sev_es_setup_ap_jump_table(struct real_mode_header *rmh);
+void sev_es_nmi_enter(void);
#else /* CONFIG_AMD_MEM_ENCRYPT */
static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh)
{
return 0;
}
+static inline void sev_es_nmi_enter(void) { }
+#endif /* CONFIG_AMD_MEM_ENCRYPT*/
+
+#else /* !__ASSEMBLY__ */
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+#define SEV_ES_NMI_COMPLETE \
+ ALTERNATIVE "", "callq sev_es_nmi_complete", X86_FEATURE_SEV_ES_GUEST
+
+.macro SEV_ES_IRET_CHECK
+ ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_SEV_ES_GUEST
+ movq PER_CPU_VAR(sev_es_in_nmi), %rdi
+ testq %rdi, %rdi
+ jz .Lend_\@
+ callq sev_es_nmi_complete
+.Lend_\@:
+.endm
+
+#else /* CONFIG_AMD_MEM_ENCRYPT */
+#define SEV_ES_NMI_COMPLETE
+.macro SEV_ES_IRET_CHECK
+.endm
#endif /* CONFIG_AMD_MEM_ENCRYPT*/

+#endif /* __ASSEMBLY__ */
+
#endif
diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
index 20a05839dd9a..0f837339db66 100644
--- a/arch/x86/include/uapi/asm/svm.h
+++ b/arch/x86/include/uapi/asm/svm.h
@@ -84,6 +84,7 @@
/* SEV-ES software-defined VMGEXIT events */
#define SVM_VMGEXIT_MMIO_READ 0x80000001
#define SVM_VMGEXIT_MMIO_WRITE 0x80000002
+#define SVM_VMGEXIT_NMI_COMPLETE 0x80000003
#define SVM_VMGEXIT_AP_HLT_LOOP 0x80000004
#define SVM_VMGEXIT_AP_JUMP_TABLE 0x80000005
#define SVM_VMGEXIT_SET_AP_JUMP_TABLE 0
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 54c21d6abd5a..7312a6d4d50f 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -37,6 +37,7 @@
#include <asm/reboot.h>
#include <asm/cache.h>
#include <asm/nospec-branch.h>
+#include <asm/sev-es.h>

#define CREATE_TRACE_POINTS
#include <trace/events/nmi.h>
@@ -510,6 +511,13 @@ NOKPROBE_SYMBOL(is_debug_stack);
dotraplinkage notrace void
do_nmi(struct pt_regs *regs, long error_code)
{
+ /*
+ * For SEV-ES the kernel needs to track whether NMIs are blocked until
+ * IRET is reached, even when the CPU is offline.
+ */
+ if (sev_es_active())
+ sev_es_nmi_enter();
+
if (IS_ENABLED(CONFIG_SMP) && cpu_is_offline(smp_processor_id()))
return;

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 3c22f256645e..409a7a2aa630 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -37,6 +37,7 @@ struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
*/
struct ghcb __initdata *boot_ghcb;
static DEFINE_PER_CPU(unsigned long, cached_dr7) = DR7_RESET_VALUE;
+DEFINE_PER_CPU(bool, sev_es_in_nmi) = false;

struct ghcb_state {
struct ghcb *ghcb;
@@ -270,6 +271,31 @@ static phys_addr_t vc_slow_virt_to_phys(struct ghcb *ghcb, long vaddr)
/* Include code shared with pre-decompression boot stage */
#include "sev-es-shared.c"

+void sev_es_nmi_enter(void)
+{
+ this_cpu_write(sev_es_in_nmi, true);
+}
+
+void sev_es_nmi_complete(void)
+{
+ struct ghcb_state state;
+ struct ghcb *ghcb;
+
+ ghcb = sev_es_get_ghcb(&state);
+
+ vc_ghcb_invalidate(ghcb);
+ ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_NMI_COMPLETE);
+ ghcb_set_sw_exit_info_1(ghcb, 0);
+ ghcb_set_sw_exit_info_2(ghcb, 0);
+
+ sev_es_wr_ghcb_msr(__pa(ghcb));
+ VMGEXIT();
+
+ sev_es_put_ghcb(&state);
+
+ this_cpu_write(sev_es_in_nmi, false);
+}
+
static u64 sev_es_get_jump_table_addr(void)
{
struct ghcb_state state;
@@ -891,7 +917,10 @@ static enum es_result vc_handle_vmmcall(struct ghcb *ghcb,
static enum es_result vc_handle_db_exception(struct ghcb *ghcb,
struct es_em_ctxt *ctxt)
{
- do_debug(ctxt->regs, 0);
+ if (this_cpu_read(sev_es_in_nmi))
+ sev_es_nmi_complete();
+ else
+ do_debug(ctxt->regs, 0);

/* Exception event, do not advance RIP */
return ES_RETRY;
--
2.17.1