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SubjectRe: [RFC PATCH V3 13/16] x86/sev: Add Check of #HV event in path
From
On 1/22/2023 3:46 AM, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@microsoft.com>
>
> Add check_hv_pending() and check_hv_pending_after_irq() to
> check queued #HV event when irq is disabled.
>
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
> arch/x86/entry/entry_64.S | 18 +++++++++++++++
> arch/x86/include/asm/irqflags.h | 10 +++++++++
> arch/x86/kernel/sev.c | 39 +++++++++++++++++++++++++++++++++
> 3 files changed, 67 insertions(+)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 6baec7653f19..aec8dc4443d1 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1064,6 +1064,15 @@ 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
>
> /*
> @@ -1188,6 +1197,15 @@ SYM_CODE_START(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..fe46e59168dd 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -14,6 +14,10 @@
> /*
> * Interrupt control:
> */
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +void check_hv_pending(struct pt_regs *regs);
> +void check_hv_pending_irq_enable(void);
> +#endif
>
> /* Declaration required for gcc < 4.9 to prevent -Werror=missing-prototypes */
> extern inline unsigned long native_save_fl(void);
> @@ -43,12 +47,18 @@ 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_irq_enable();
> +#endif
> }
>
> static inline __cpuidle void native_safe_halt(void)
> {
> mds_idle_clear_cpu_buffers();
> asm volatile("sti; hlt": : :"memory");
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> + check_hv_pending_irq_enable();
> +#endif
> }
>
> static inline __cpuidle void native_halt(void)
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index a8862a2eff67..fe5e5e41433d 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -179,6 +179,45 @@ 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)
> + return;

Will this return and prevent guest from executing NMI's
while irqs are disabled?

Thanks,
Pankaj

> +
> + do_exc_hv(regs);
> +}
> +
> +void check_hv_pending_irq_enable(void)
> +{
> + unsigned long flags;
> + struct pt_regs regs;
> +
> + if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> + return;
> +
> + memset(&regs, 0, sizeof(struct pt_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();
> +
> + /*
> + * Disable irq when handle pending #HV events after
> + * re-enabling irq.
> + */
> + asm volatile("cli" : : : "memory");
> + do_exc_hv(&regs);
> + asm volatile("sti" : : : "memory");
> +}
> +
> void noinstr __sev_es_ist_exit(void)
> {
> unsigned long ist;

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