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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jane Malalane <jane.malalane@citrix.com>,
	LKML <linux-kernel@vger.kernel.org>
Cc: <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>, Pu Wen <puwen@hygon.cn>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Yazen Ghannam <Yazen.Ghannam@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Huang Rui <ray.huang@amd.com>, Andy Lutomirski <luto@kernel.org>,
	Kim Phillips <kim.phillips@amd.com>, <stable@vger.kernel.org>
Subject: Re: [PATCH] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL
Date: Fri, 1 Oct 2021 15:07:34 +0100	[thread overview]
Message-ID: <68a9f1b7-0d8e-b25f-8330-345c039277b0@citrix.com> (raw)
In-Reply-To: <20211001133349.9825-1-jane.malalane@citrix.com>

On 01/10/2021 14:33, Jane Malalane wrote:
> Currently, Linux probes for X86_BUG_NULL_SEL unconditionally which
> makes it unsafe to migrate in a virtualised environment as the
> properties across the migration pool might differ.
>
> Zen3 adds the NullSelectorClearsBase bit to indicate that loading
> a NULL segment selector zeroes the base and limit fields, as well as
> just attributes. Zen2 also has this behaviour but doesn't have the
> NSCB bit.
>
> When virtualised, NSCB might be cleared for migration safety,
> therefore we must not probe. Always honour the NSCB bit in this case,
> as the hypervisor is expected to synthesize it in the Zen2 case.
>
> Signed-off-by: Jane Malalane <jane.malalane@citrix.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>


  reply	other threads:[~2021-10-01 14:15 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-01 13:33 Jane Malalane
2021-10-01 14:07 ` Andrew Cooper [this message]
2021-10-01 14:19 ` Borislav Petkov
2021-10-06 14:15   ` Andrew Cooper
2021-10-06 14:30     ` Borislav Petkov
2021-10-05 20:58 ` Andy Lutomirski

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