RE: [RFC PATCH V4 14/17] x86/hyperv/sev: Add AMD sev-snp enlightened guest support on hyperv

From: Michael Kelley (LINUX)
Date: Wed Apr 12 2023 - 11:02:49 EST

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From: Tianyu Lan <ltykernel@xxxxxxxxx> Sent: Monday, April 3, 2023 10:44 AM
>

The patch subject prefix of "x86/hyperv/sev:" doesn't make sense.
There's no pathname like that in the kernel code. I think it should just be
"x86/sev:".

> Enable #HV exception to handle interrupt requests from hypervisor.
>
> Co-developed-by: Lendacky Thomas <thomas.lendacky@xxxxxxx>
> Co-developed-by: Kalra Ashish <ashish.kalra@xxxxxxx>
> Signed-off-by: Tianyu Lan <tiala@xxxxxxxxxxxxx>
> ---
> Change since RFC V3:
> * Check NMI event when irq is disabled.
> * Remove redundant variable
> ---
> arch/x86/include/asm/mem_encrypt.h | 2 +
> arch/x86/include/uapi/asm/svm.h | 4 +
> arch/x86/kernel/sev.c | 314 ++++++++++++++++++++++++-----
> arch/x86/kernel/traps.c | 2 +
> 4 files changed, 266 insertions(+), 56 deletions(-)
>
> diff --git a/arch/x86/include/asm/mem_encrypt.h
> b/arch/x86/include/asm/mem_encrypt.h
> index b7126701574c..9299caeca69f 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -50,6 +50,7 @@ void __init early_set_mem_enc_dec_hypercall(unsigned long
> vaddr, int npages,
> void __init mem_encrypt_free_decrypted_mem(void);
>
> void __init sev_es_init_vc_handling(void);
> +void __init sev_snp_init_hv_handling(void);
>
> #define __bss_decrypted __section(".bss..decrypted")
>
> @@ -73,6 +74,7 @@ static inline void __init sme_encrypt_kernel(struct boot_params
> *bp) { }
> static inline void __init sme_enable(struct boot_params *bp) { }
>
> static inline void sev_es_init_vc_handling(void) { }
> +static inline void sev_snp_init_hv_handling(void) { }
>
> static inline int __init
> early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0; }
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index 80e1df482337..828d624a38cf 100644
> --- a/arch/x86/include/uapi/asm/svm.h
> +++ b/arch/x86/include/uapi/asm/svm.h
> @@ -115,6 +115,10 @@
> #define SVM_VMGEXIT_AP_CREATE_ON_INIT 0
> #define SVM_VMGEXIT_AP_CREATE 1
> #define SVM_VMGEXIT_AP_DESTROY 2
> +#define SVM_VMGEXIT_HV_DOORBELL_PAGE 0x80000014
> +#define SVM_VMGEXIT_GET_PREFERRED_HV_DOORBELL_PAGE 0
> +#define SVM_VMGEXIT_SET_HV_DOORBELL_PAGE 1
> +#define SVM_VMGEXIT_QUERY_HV_DOORBELL_PAGE 2
> #define SVM_VMGEXIT_HV_FEATURES 0x8000fffd
> #define SVM_VMGEXIT_TERM_REQUEST 0x8000fffe
> #define SVM_VMGEXIT_TERM_REASON(reason_set, reason_code) \
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 6445f5356c45..7fcb3b548215 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -122,6 +122,152 @@ struct sev_config {
>
> static struct sev_config sev_cfg __read_mostly;
>
> +static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state);
> +static noinstr void __sev_put_ghcb(struct ghcb_state *state);
> +static int vmgexit_hv_doorbell_page(struct ghcb *ghcb, u64 op, u64 pa);
> +static void sev_snp_setup_hv_doorbell_page(struct ghcb *ghcb);
> +
> +union hv_pending_events {
> + u16 events;
> + struct {
> + u8 vector;
> + u8 nmi : 1;
> + u8 mc : 1;
> + u8 reserved1 : 5;
> + u8 no_further_signal : 1;
> + };
> +};
> +
> +struct sev_hv_doorbell_page {
> + union hv_pending_events pending_events;
> + u8 no_eoi_required;
> + u8 reserved2[61];
> + u8 padding[4032];
> +};
> +
> +struct sev_snp_runtime_data {
> + struct sev_hv_doorbell_page hv_doorbell_page;
> +};
> +
> +static DEFINE_PER_CPU(struct sev_snp_runtime_data*, snp_runtime_data);
> +
> +static inline u64 sev_es_rd_ghcb_msr(void)
> +{
> + return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
> +}
> +
> +static __always_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);
> +}
> +
> +struct sev_hv_doorbell_page *sev_snp_current_doorbell_page(void)
> +{
> + return &this_cpu_read(snp_runtime_data)->hv_doorbell_page;
> +}
> +
> +static u8 sev_hv_pending(void)
> +{
> + return sev_snp_current_doorbell_page()->pending_events.events;
> +}
> +
> +#define sev_hv_pending_nmi \
> + sev_snp_current_doorbell_page()->pending_events.nmi
> +
> +static void hv_doorbell_apic_eoi_write(u32 reg, u32 val)
> +{
> + if (xchg(&sev_snp_current_doorbell_page()->no_eoi_required, 0) & 0x1)
> + return;
> +
> + BUG_ON(reg != APIC_EOI);
> + apic->write(reg, val);
> +}
> +
> +static void do_exc_hv(struct pt_regs *regs)
> +{
> + union hv_pending_events pending_events;
> +
> + while (sev_hv_pending()) {
> + pending_events.events = xchg(
> + &sev_snp_current_doorbell_page()->pending_events.events,
> + 0);
> +
> + if (pending_events.nmi)
> + exc_nmi(regs);
> +
> +#ifdef CONFIG_X86_MCE
> + if (pending_events.mc)
> + exc_machine_check(regs);
> +#endif
> +
> + if (!pending_events.vector)
> + return;
> +
> + if (pending_events.vector < FIRST_EXTERNAL_VECTOR) {
> + /* Exception vectors */
> + WARN(1, "exception shouldn't happen\n");
> + } else if (pending_events.vector == FIRST_EXTERNAL_VECTOR) {
> + sysvec_irq_move_cleanup(regs);
> + } else if (pending_events.vector == IA32_SYSCALL_VECTOR) {
> + WARN(1, "syscall shouldn't happen\n");
> + } else if (pending_events.vector >= FIRST_SYSTEM_VECTOR) {
> + switch (pending_events.vector) {
> +#if IS_ENABLED(CONFIG_HYPERV)
> + case HYPERV_STIMER0_VECTOR:
> + sysvec_hyperv_stimer0(regs);
> + break;
> + case HYPERVISOR_CALLBACK_VECTOR:
> + sysvec_hyperv_callback(regs);
> + break;
> +#endif
> +#ifdef CONFIG_SMP
> + case RESCHEDULE_VECTOR:
> + sysvec_reschedule_ipi(regs);
> + break;
> + case IRQ_MOVE_CLEANUP_VECTOR:
> + sysvec_irq_move_cleanup(regs);
> + break;
> + case REBOOT_VECTOR:
> + sysvec_reboot(regs);
> + break;
> + case CALL_FUNCTION_SINGLE_VECTOR:
> + sysvec_call_function_single(regs);
> + break;
> + case CALL_FUNCTION_VECTOR:
> + sysvec_call_function(regs);
> + break;
> +#endif
> +#ifdef CONFIG_X86_LOCAL_APIC
> + case ERROR_APIC_VECTOR:
> + sysvec_error_interrupt(regs);
> + break;
> + case SPURIOUS_APIC_VECTOR:
> + sysvec_spurious_apic_interrupt(regs);
> + break;
> + case LOCAL_TIMER_VECTOR:
> + sysvec_apic_timer_interrupt(regs);
> + break;
> + case X86_PLATFORM_IPI_VECTOR:
> + sysvec_x86_platform_ipi(regs);
> + break;
> +#endif
> + case 0x0:
> + break;
> + default:
> + panic("Unexpected vector %d\n", vector);
> + unreachable();
> + }
> + } else {
> + common_interrupt(regs, pending_events.vector);
> + }
> + }
> +}
> +
> static __always_inline bool on_vc_stack(struct pt_regs *regs)
> {
> unsigned long sp = regs->sp;
> @@ -179,18 +325,19 @@ void noinstr __sev_es_ist_enter(struct pt_regs *regs)
> this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], new_ist);
> }
>
> -static void do_exc_hv(struct pt_regs *regs)
> -{
> - /* Handle #HV exception. */
> -}
> -
> void check_hv_pending(struct pt_regs *regs)
> {
> if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> return;
>
> - if ((regs->flags & X86_EFLAGS_IF) == 0)
> + /* Handle NMI when irq is disabled. */
> + if ((regs->flags & X86_EFLAGS_IF) == 0) {
> + if (sev_hv_pending_nmi) {
> + exc_nmi(regs);
> + sev_hv_pending_nmi = 0;
> + }
> return;
> + }
>
> do_exc_hv(regs);
> }
> @@ -231,68 +378,35 @@ void noinstr __sev_es_ist_exit(void)
> this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
> }
>
> -/*
> - * Nothing shall interrupt this code path while holding the per-CPU
> - * GHCB. The backup GHCB is only for NMIs interrupting this path.
> - *
> - * Callers must disable local interrupts around it.
> - */
> -static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
> +static bool sev_restricted_injection_enabled(void)
> +{
> + return sev_status & MSR_AMD64_SNP_RESTRICTED_INJ;
> +}
> +
> +void __init sev_snp_init_hv_handling(void)
> {
> struct sev_es_runtime_data *data;
> + struct ghcb_state state;
> struct ghcb *ghcb;
> + unsigned long flags;
>
> WARN_ON(!irqs_disabled());
> + if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP) ||
> !sev_restricted_injection_enabled())
> + return;
>
> data = this_cpu_read(runtime_data);
> - ghcb = &data->ghcb_page;
> -
> - if (unlikely(data->ghcb_active)) {
> - /* GHCB is already in use - save its contents */
> -
> - if (unlikely(data->backup_ghcb_active)) {
> - /*
> - * Backup-GHCB is also already in use. There is no way
> - * to continue here so just kill the machine. To make
> - * panic() work, mark GHCBs inactive so that messages
> - * can be printed out.
> - */
> - data->ghcb_active = false;
> - data->backup_ghcb_active = false;
> -
> - instrumentation_begin();
> - panic("Unable to handle #VC exception! GHCB and Backup
> GHCB are already in use");
> - instrumentation_end();
> - }
> -
> - /* Mark backup_ghcb active before writing to it */
> - data->backup_ghcb_active = true;
>
> - state->ghcb = &data->backup_ghcb;
> + local_irq_save(flags);
>
> - /* Backup GHCB content */
> - *state->ghcb = *ghcb;
> - } else {
> - state->ghcb = NULL;
> - data->ghcb_active = true;
> - }
> + ghcb = __sev_get_ghcb(&state);
>
> - return ghcb;
> -}
> + sev_snp_setup_hv_doorbell_page(ghcb);
>
> -static inline u64 sev_es_rd_ghcb_msr(void)
> -{
> - return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
> -}
> -
> -static __always_inline void sev_es_wr_ghcb_msr(u64 val)
> -{
> - u32 low, high;
> + __sev_put_ghcb(&state);
>
> - low = (u32)(val);
> - high = (u32)(val >> 32);
> + apic_set_eoi_write(hv_doorbell_apic_eoi_write);
>
> - native_wrmsr(MSR_AMD64_SEV_ES_GHCB, low, high);
> + local_irq_restore(flags);
> }
>
> static int vc_fetch_insn_kernel(struct es_em_ctxt *ctxt,
> @@ -553,6 +667,69 @@ static enum es_result vc_slow_virt_to_phys(struct ghcb
> *ghcb, struct es_em_ctxt
> /* Include code shared with pre-decompression boot stage */
> #include "sev-shared.c"
>
> +/*
> + * Nothing shall interrupt this code path while holding the per-CPU
> + * GHCB. The backup GHCB is only for NMIs interrupting this path.
> + *
> + * Callers must disable local interrupts around it.
> + */
> +static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
> +{
> + struct sev_es_runtime_data *data;
> + struct ghcb *ghcb;
> +
> + WARN_ON(!irqs_disabled());
> +
> + data = this_cpu_read(runtime_data);
> + ghcb = &data->ghcb_page;
> +
> + if (unlikely(data->ghcb_active)) {
> + /* GHCB is already in use - save its contents */
> +
> + if (unlikely(data->backup_ghcb_active)) {
> + /*
> + * Backup-GHCB is also already in use. There is no way
> + * to continue here so just kill the machine. To make
> + * panic() work, mark GHCBs inactive so that messages
> + * can be printed out.
> + */
> + data->ghcb_active = false;
> + data->backup_ghcb_active = false;
> +
> + instrumentation_begin();
> + panic("Unable to handle #VC exception! GHCB and Backup
> GHCB are already in use");
> + instrumentation_end();
> + }
> +
> + /* Mark backup_ghcb active before writing to it */
> + data->backup_ghcb_active = true;
> +
> + state->ghcb = &data->backup_ghcb;
> +
> + /* Backup GHCB content */
> + *state->ghcb = *ghcb;
> + } else {
> + state->ghcb = NULL;
> + data->ghcb_active = true;
> + }
> +
> + return ghcb;
> +}
> +
> +static void sev_snp_setup_hv_doorbell_page(struct ghcb *ghcb)
> +{
> + u64 pa;
> + enum es_result ret;
> +
> + pa = __pa(sev_snp_current_doorbell_page());
> + vc_ghcb_invalidate(ghcb);
> + ret = vmgexit_hv_doorbell_page(ghcb,
> + SVM_VMGEXIT_SET_HV_DOORBELL_PAGE,
> + pa);
> + if (ret != ES_OK)
> + panic("SEV-SNP: failed to set up #HV doorbell page");
> +}
> +
> static noinstr void __sev_put_ghcb(struct ghcb_state *state)
> {
> struct sev_es_runtime_data *data;
> @@ -1281,6 +1458,7 @@ static void snp_register_per_cpu_ghcb(void)
> ghcb = &data->ghcb_page;
>
> snp_register_ghcb_early(__pa(ghcb));
> + sev_snp_setup_hv_doorbell_page(ghcb);
> }
>
> void setup_ghcb(void)
> @@ -1320,6 +1498,11 @@ void setup_ghcb(void)
> snp_register_ghcb_early(__pa(&boot_ghcb_page));
> }
>
> +int vmgexit_hv_doorbell_page(struct ghcb *ghcb, u64 op, u64 pa)
> +{
> + return sev_es_ghcb_hv_call(ghcb, NULL, SVM_VMGEXIT_HV_DOORBELL_PAGE,
> op, pa);
> +}
> +
> #ifdef CONFIG_HOTPLUG_CPU
> static void sev_es_ap_hlt_loop(void)
> {
> @@ -1393,6 +1576,7 @@ static void __init alloc_runtime_data(int cpu)
> static void __init init_ghcb(int cpu)
> {
> struct sev_es_runtime_data *data;
> + struct sev_snp_runtime_data *snp_data;
> int err;
>
> data = per_cpu(runtime_data, cpu);
> @@ -1404,6 +1588,19 @@ static void __init init_ghcb(int cpu)
>
> memset(&data->ghcb_page, 0, sizeof(data->ghcb_page));
>
> + snp_data = memblock_alloc(sizeof(*snp_data), PAGE_SIZE);
> + if (!snp_data)
> + panic("Can't allocate SEV-SNP runtime data");
> +
> + err = early_set_memory_decrypted((unsigned long)&snp_data-
> >hv_doorbell_page,
> + sizeof(snp_data->hv_doorbell_page));
> + if (err)
> + panic("Can't map #HV doorbell pages unencrypted");
> +
> + memset(&snp_data->hv_doorbell_page, 0, sizeof(snp_data-
> >hv_doorbell_page));
> +
> + per_cpu(snp_runtime_data, cpu) = snp_data;
> +
> data->ghcb_active = false;
> data->backup_ghcb_active = false;
> }
> @@ -2044,7 +2241,12 @@ DEFINE_IDTENTRY_VC_USER(exc_vmm_communication)
>
> static bool hv_raw_handle_exception(struct pt_regs *regs)
> {
> - return false;
> + /* Clear the no_further_signal bit */
> + sev_snp_current_doorbell_page()->pending_events.events &= 0x7fff;
> +
> + check_hv_pending(regs);
> +
> + return true;
> }
>
> static __always_inline bool on_hv_fallback_stack(struct pt_regs *regs)
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index d29debec8134..1aa6cab2394b 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -1503,5 +1503,7 @@ void __init trap_init(void)
> cpu_init_exception_handling();
> /* Setup traps as cpu_init() might #GP */
> idt_setup_traps();
> + sev_snp_init_hv_handling();
> +
> cpu_init();
> }
> --
> 2.25.1

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