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Date:   Thu, 26 Oct 2023 19:25:27 +0300
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Subject: Re: [PATCH v3 2/6] x86/entry_64: Add VERW just before userspace
 transition
Content-Language: en-US
To:     Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>, tony.luck@intel.com,
        ak@linux.intel.com, tim.c.chen@linux.intel.com
Cc:     linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        kvm@vger.kernel.org,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        antonio.gomez.iglesias@linux.intel.com,
        Dave Hansen <dave.hansen@intel.com>
References: <20231025-delay-verw-v3-0-52663677ee35@linux.intel.com>
 <20231025-delay-verw-v3-2-52663677ee35@linux.intel.com>
From:   Nikolay Borisov <nik.borisov@suse.com>
In-Reply-To: <20231025-delay-verw-v3-2-52663677ee35@linux.intel.com>
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On 25.10.23 г. 23:52 ч., Pawan Gupta wrote:

<snip>

> @@ -1520,6 +1530,7 @@ SYM_CODE_START(ignore_sysret)
>   	UNWIND_HINT_END_OF_STACK
>   	ENDBR
>   	mov	$-ENOSYS, %eax
> +	CLEAR_CPU_BUFFERS

nit: Just out of curiosity is it really needed in this case or it's 
doesn for the sake of uniformity so that all ring3 transitions are 
indeed covered??

>   	sysretl
>   SYM_CODE_END(ignore_sysret)
>   #endif
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index 70150298f8bd..245697eb8485 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -271,6 +271,7 @@ SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
>   	xorl	%r9d, %r9d
>   	xorl	%r10d, %r10d
>   	swapgs
> +	CLEAR_CPU_BUFFERS
>   	sysretl
>   SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
>   	ANNOTATE_NOENDBR
>