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From: Kim Phillips <kim.phillips@amd.com>
To: Jim Mattson <jmattson@google.com>
Cc: <x86@kernel.org>, Tom Lendacky <thomas.lendacky@amd.com>,
	Borislav Petkov <bp@alien8.de>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Joao Martins <joao.m.martins@oracle.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Juergen Gross <jgross@suse.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Tony Luck <tony.luck@intel.com>,
	Alexey Kardashevskiy <aik@amd.com>, <kvm@vger.kernel.org>,
	<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<stable@vger.kernel.org>
Subject: Re: [PATCH] x86/cpu: Enable STIBP if Automatic IBRS is enabled
Date: Thu, 20 Jul 2023 16:53:23 -0500	[thread overview]
Message-ID: <6a43b05b-ffdd-0e6f-56a0-5b78532ee383@amd.com> (raw)
In-Reply-To: <CALMp9eTBWWcApb50432zZEGg+PMCzUELaZvdkzYngNSrriimWA@mail.gmail.com>

On 7/20/23 3:58 PM, Jim Mattson wrote:
> On Thu, Jul 20, 2023 at 12:48 PM Kim Phillips <kim.phillips@amd.com> wrote:
>>
>> Unlike Intel's Enhanced IBRS feature, AMD's Automatic IBRS does not
>> provide protection to processes running at CPL3/user mode [1].
>>
>> Explicitly enable STIBP to protect against cross-thread CPL3
>> branch target injections on systems with Automatic IBRS enabled.
> 
> Is there any performance penalty to enabling STIBP + AUTOIBRS, aside
> from the lost sharing?

Not to my knowledge.

> Or does this just effectively tag the branch
> prediction information with thread ID?

I don't know the implementation, but AFAIK, AUTOIBRS and STIBP
are independent of each other.

Thanks,

Kim

  reply	other threads:[~2023-07-20 21:53 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-20 19:47 Kim Phillips
2023-07-20 20:58 ` Jim Mattson
2023-07-20 21:53   ` Kim Phillips [this message]
2023-07-22 16:18 ` [tip: x86/urgent] x86/cpu: Enable STIBP on AMD " tip-bot2 for Kim Phillips

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