Re: [RFC PATCH V2 16/18] x86/sev: Initialize #HV doorbell and handle interrupt requests
From: Christophe de Dinechin
Date: Fri Nov 25 2022 - 10:13:17 EST
On 2022-11-18 at 22:46 -05, Tianyu Lan <ltykernel@xxxxxxxxx> wrote...
> From: Tianyu Lan <tiala@xxxxxxxxxxxxx>
>
> 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>
> ---
> arch/x86/entry/entry_64.S | 18 ++
> arch/x86/include/asm/irqflags.h | 19 ++
> arch/x86/include/asm/mem_encrypt.h | 2 +
> arch/x86/include/asm/msr-index.h | 6 +
> arch/x86/include/uapi/asm/svm.h | 4 +
> arch/x86/kernel/sev.c | 354 ++++++++++++++++++++++++-----
> arch/x86/kernel/traps.c | 50 ++++
> 7 files changed, 400 insertions(+), 53 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index b2059df43c57..fe460cf44ab5 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1058,6 +1058,15 @@ SYM_CODE_END(paranoid_entry)
> * R15 - old SPEC_CTRL
> */
> SYM_CODE_START_LOCAL(paranoid_exit)
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> + /*
> + * If a #HV was delivered during execution and interrupts were
> + * disabled, then check if it can be handled before the iret
> + * (which may re-enable interrupts).
> + */
> + mov %rsp, %rdi
> + call check_hv_pending
> +#endif
> UNWIND_HINT_REGS
>
> /*
> @@ -1183,6 +1192,15 @@ SYM_CODE_START_LOCAL(error_entry)
> SYM_CODE_END(error_entry)
>
> SYM_CODE_START_LOCAL(error_return)
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> + /*
> + * If a #HV was delivered during execution and interrupts were
> + * disabled, then check if it can be handled before the iret
> + * (which may re-enable interrupts).
> + */
> + mov %rsp, %rdi
> + call check_hv_pending
> +#endif
> UNWIND_HINT_REGS
> DEBUG_ENTRY_ASSERT_IRQS_OFF
> testb $3, CS(%rsp)
> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
> index 7793e52d6237..e0730d8bc0ac 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -14,6 +14,9 @@
> /*
> * Interrupt control:
> */
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +void check_hv_pending(struct pt_regs *regs);
> +#endif
>
> /* Declaration required for gcc < 4.9 to prevent -Werror=missing-prototypes */
> extern inline unsigned long native_save_fl(void);
> @@ -35,6 +38,19 @@ extern __always_inline unsigned long native_save_fl(void)
> return flags;
> }
>
> +extern inline void native_restore_fl(unsigned long flags)
> +{
> + asm volatile("push %0 ; popf"
> + : /* no output */
> + : "g" (flags)
> + : "memory", "cc");
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> + if ((flags & X86_EFLAGS_IF)) {
> + check_hv_pending(NULL);
> + }
> +#endif
> +}
> +
> static __always_inline void native_irq_disable(void)
> {
> asm volatile("cli": : :"memory");
> @@ -43,6 +59,9 @@ static __always_inline void native_irq_disable(void)
> static __always_inline void native_irq_enable(void)
> {
> asm volatile("sti": : :"memory");
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> + check_hv_pending(NULL);
> +#endif
> }
>
> static inline __cpuidle void native_safe_halt(void)
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 72ca90552b6a..7264ca5f5b2d 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")
>
> @@ -72,6 +73,7 @@ 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/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 10ac52705892..6fe25a6e325f 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -562,10 +562,16 @@
> #define MSR_AMD64_SEV_ENABLED_BIT 0
> #define MSR_AMD64_SEV_ES_ENABLED_BIT 1
> #define MSR_AMD64_SEV_SNP_ENABLED_BIT 2
> +#define MSR_AMD64_SEV_REFLECTVC_ENABLED_BIT 4
> +#define MSR_AMD64_SEV_RESTRICTED_INJECTION_ENABLED_BIT 5
> +#define MSR_AMD64_SEV_ALTERNATE_INJECTION_ENABLED_BIT 6
> #define MSR_AMD64_SEV_ENABLED BIT_ULL(MSR_AMD64_SEV_ENABLED_BIT)
> #define MSR_AMD64_SEV_ES_ENABLED BIT_ULL(MSR_AMD64_SEV_ES_ENABLED_BIT)
> #define MSR_AMD64_SEV_SNP_ENABLED BIT_ULL(MSR_AMD64_SEV_SNP_ENABLED_BIT)
>
> +#define MSR_AMD64_SEV_REFLECTVC_ENABLED BIT_ULL(MSR_AMD64_SEV_REFLECTVC_ENABLED_BIT)
> +#define MSR_AMD64_SEV_RESTRICTED_INJECTION_ENABLED BIT_ULL(MSR_AMD64_SEV_RESTRICTED_INJECTION_ENABLED_BIT)
> +#define MSR_AMD64_SEV_ALTERNATE_INJECTION_ENABLED BIT_ULL(MSR_AMD64_SEV_ALTERNATE_INJECTION_ENABLED_BIT)
> #define MSR_AMD64_VIRT_SPEC_CTRL 0xc001011f
>
> /* AMD Collaborative Processor Performance Control MSRs */
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index f69c168391aa..85d6882262e7 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_UNSUPPORTED_EVENT 0x8000ffff
>
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index b54ee3ba37b0..23cd025f97dc 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -104,6 +104,12 @@ 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 {
> @@ -122,6 +128,183 @@ 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;
> +}
> +
> +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;
> + u8 vector;
> +
> + while (sev_hv_pending()) {
> + asm volatile("cli" : : : "memory");
> +
> + 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);
> + }
> +
> + asm volatile("sti" : : : "memory");
> + }
> +}
> +
> +void check_hv_pending(struct pt_regs *regs)
This looks like two functions, one with regs == NULL and one with regs,
different internal logic, different call sites. Would you consider splitting
into two?
> +{
> + struct pt_regs local_regs;
> +
> + if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> + return;
> +
> + if (regs) {
> + if ((regs->flags & X86_EFLAGS_IF) == 0)
> + return;
> +
> + if (!sev_hv_pending())
> + return;
> +
> + do_exc_hv(regs);
> + } else {
> + if (sev_hv_pending()) {
> + memset(&local_regs, 0, sizeof(struct pt_regs));
> + regs = &local_regs;
> + asm volatile("movl %%cs, %%eax;" : "=a" (regs->cs));
> + asm volatile("movl %%ss, %%eax;" : "=a" (regs->ss));
> + regs->orig_ax = 0xffffffff;
> + regs->flags = native_save_fl();
> + do_exc_hv(regs);
> + }
> + }
> +}
> +EXPORT_SYMBOL_GPL(check_hv_pending);
> +
> static __always_inline bool on_vc_stack(struct pt_regs *regs)
> {
> unsigned long sp = regs->sp;
> @@ -193,68 +376,35 @@ 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)
> {
> - struct sev_es_runtime_data *data;
> + return sev_status & MSR_AMD64_SEV_RESTRICTED_INJECTION_ENABLED;
> +}
> +
> +void __init sev_snp_init_hv_handling(void)
> +{
> + struct sev_snp_runtime_data *snp_data;
> + struct ghcb_state state;
> struct ghcb *ghcb;
> + unsigned long flags;
> + int cpu;
> + int err;
>
> 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;
> -
> - /* Backup GHCB content */
> - *state->ghcb = *ghcb;
> - } else {
> - state->ghcb = NULL;
> - data->ghcb_active = true;
> - }
> + local_irq_save(flags);
>
> - return ghcb;
> -}
> + ghcb = __sev_get_ghcb(&state);
>
> -static inline u64 sev_es_rd_ghcb_msr(void)
> -{
> - return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
> -}
> + sev_snp_setup_hv_doorbell_page(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,
> @@ -515,6 +665,79 @@ 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;
> + }
> +
> + /* SEV-SNP guest requires that GHCB must be registered before using it. */
> + if (!data->ghcb_registered) {
> + if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {
> + snp_register_ghcb_early(__pa(ghcb));
> + sev_snp_setup_hv_doorbell_page(ghcb);
> + } else {
> + sev_es_wr_ghcb_msr(__pa(ghcb));
> + }
> + data->ghcb_registered = 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;
> @@ -1282,6 +1505,11 @@ 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)
> {
> @@ -1355,6 +1583,7 @@ 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);
> @@ -1366,8 +1595,22 @@ 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;
> + data->ghcb_registered = false;
> }
>
> void __init sev_es_init_vc_handling(void)
> @@ -2006,7 +2249,12 @@ 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 178015a820f0..af97e6610fbb 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -898,6 +898,53 @@ asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *r
>
> return regs_ret;
> }
> +
> +asmlinkage __visible noinstr struct pt_regs *hv_switch_off_ist(struct pt_regs *regs)
> +{
> + unsigned long sp, *stack;
> + struct stack_info info;
> + struct pt_regs *regs_ret;
> +
> + /*
> + * A malicious hypervisor can inject 2 HVs in a row, which will corrupt
> + * the trap frame on our IST stack. We add a defensive check here to
> + * catch such behavior.
> + */
> + BUG_ON(regs->sp >= __this_cpu_ist_bottom_va(HV) && regs->sp < __this_cpu_ist_top_va(HV));
> +
> + /*
> + * In the SYSCALL entry path the RSP value comes from user-space - don't
> + * trust it and switch to the current kernel stack
> + */
> + if (ip_within_syscall_gap(regs)) {
> + sp = this_cpu_read(cpu_current_top_of_stack);
> + goto sync;
> + }
> +
> + /*
> + * From here on the RSP value is trusted. Now check whether entry
> + * happened from a safe stack. Not safe are the entry or unknown stacks,
> + * use the fall-back stack instead in this case.
> + */
> + sp = regs->sp;
> + stack = (unsigned long *)sp;
> +
> + if (!get_stack_info_noinstr(stack, current, &info) || info.type == STACK_TYPE_ENTRY ||
> + info.type > STACK_TYPE_EXCEPTION_LAST)
> + sp = __this_cpu_ist_top_va(HV2);
> +sync:
> + /*
> + * Found a safe stack - switch to it as if the entry didn't happen via
> + * IST stack. The code below only copies pt_regs, the real switch happens
> + * in assembly code.
> + */
> + sp = ALIGN_DOWN(sp, 8) - sizeof(*regs_ret);
> +
> + regs_ret = (struct pt_regs *)sp;
> + *regs_ret = *regs;
> +
> + return regs_ret;
> +}
> #endif
>
> asmlinkage __visible noinstr struct pt_regs *fixup_bad_iret(struct pt_regs *bad_regs)
> @@ -1457,4 +1504,7 @@ void __init trap_init(void)
> /* Setup traps as cpu_init() might #GP */
> idt_setup_traps();
> cpu_init();
> +
> + /* Init #HV doorbell pages when running as an SEV-SNP guest */
> + sev_snp_init_hv_handling();
> }
--
Cheers,
Christophe de Dinechin (https://c3d.github.io)
Theory of Incomplete Measurements (https://c3d.github.io/TIM)