linux-kernel - Re: [RFC PATCH V4 13/17] x86/sev: Add Check of #HV event in path

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Date:   Fri, 14 Apr 2023 13:02:14 +0200
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     luto@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com,
        jgross@...e.com, tiala@...rosoft.com, kirill@...temov.name,
        jiangshan.ljs@...group.com, peterz@...radead.org,
        ashish.kalra@....com, srutherford@...gle.com,
        akpm@...ux-foundation.org, anshuman.khandual@....com,
        pawan.kumar.gupta@...ux.intel.com, adrian.hunter@...el.com,
        daniel.sneddon@...ux.intel.com, alexander.shishkin@...ux.intel.com,
        sandipan.das@....com, ray.huang@....com, brijesh.singh@....com,
        michael.roth@....com, thomas.lendacky@....com,
        venu.busireddy@...cle.com, sterritt@...gle.com,
        tony.luck@...el.com, samitolvanen@...gle.com, fenghua.yu@...el.com,
        pangupta@....com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH V4 13/17] x86/sev: Add Check of #HV event in path

> 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@...rosoft.com>
> ---
>  arch/x86/entry/entry_64.S       | 18 ++++++++++++++++
>  arch/x86/include/asm/irqflags.h | 11 ++++++++++
>  arch/x86/kernel/sev.c           | 38 +++++++++++++++++++++++++++++++++
>  3 files changed, 67 insertions(+)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index d877774c3141..efa56dfde19e 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1073,6 +1073,15 @@ 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
>
>         /*
> @@ -1197,6 +1206,15 @@ 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 8c5ae649d2df..8368e3fe2d36 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -11,6 +11,10 @@
>  /*
>   * 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);
> @@ -40,12 +44,19 @@ 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 __always_inline 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 __always_inline void native_halt(void)
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 2684a45b50a6..6445f5356c45 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -179,6 +179,44 @@ 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;
> +
> +       do_exc_hv(regs);
> +}
> +
> +void check_hv_pending_irq_enable(void)
> +{
> +       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");

Just curious, Does the hypervisor injects irqs via doorbell page when
interrupts are disabled with "cli" ? Trying to understand the need to
cli/sti covering on "do_exc_hv".

Thanks,
Pankaj

> +       do_exc_hv(&regs);
> +       asm volatile("sti" : : : "memory");
> +}
> +
>  void noinstr __sev_es_ist_exit(void)
>  {
>         unsigned long ist;
> --
> 2.25.1
>