linux-kernel - Re: [RFC PATCH V6 02/14] x86/sev: Add Check of #HV event in path

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Message-ID: <20230516093225.GD2587705@hirez.programming.kicks-ass.net>
Date:   Tue, 16 May 2023 11:32:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
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, 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 V6 02/14] x86/sev: Add Check of #HV event in path

On Mon, May 15, 2023 at 12:59:04PM -0400, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@...rosoft.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@...rosoft.com>
> ---
>  arch/x86/entry/entry_64.S       | 18 ++++++++++++++++
>  arch/x86/include/asm/irqflags.h | 14 +++++++++++-
>  arch/x86/kernel/sev.c           | 38 +++++++++++++++++++++++++++++++++
>  3 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 653b1f10699b..147b850babf6 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1019,6 +1019,15 @@ 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
>  
>  	/*
> @@ -1143,6 +1152,15 @@ 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)

Oh hell no... do now you're adding unconditional calls to every single
interrupt and nmi exit path, with the grand total of 0 justification.