Re: [RFC PATCH V3 13/16] x86/sev: Add Check of #HV event in path

["Gupta, Pankaj" <pankaj.gupta@xxxxxxx>]

On 1/22/2023 3:46 AM, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> ---
>   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;