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

Mika Penttilä
2020-03-19T16:53:45Z

Hi!

On 19.3.2020 11.14, Joerg Roedel wrote:
> 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)

What makes kernel jump here? Can't see this referenced from anywhere?

> + 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;