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Date:   Tue, 6 Jun 2023 15:03:38 -0700
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Message-ID: <ZH+tOj7lRAGsua9X@google.com>
Subject: Re: [PATCH] KVM: x86/mmu: Add "never" option to allow sticky
 disabling of nx_huge_pages
From:   Sean Christopherson <seanjc@google.com>
To:     Luiz Capitulino <luizcap@amazon.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Li RongQing <lirongqing@baidu.com>,
        Yong He <zhuangel570@gmail.com>,
        Robert Hoo <robert.hoo.linux@gmail.com>,
        Kai Huang <kai.huang@intel.com>
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On Tue, Jun 06, 2023, Luiz Capitulino wrote:
> On Thu, Jun 01, 2023 at 05:58:59PM -0700, Sean Christopherson wrote:
> However, why don't we make nx_huge_pages=never the default behavior if the
> CPU is not vulnerable?

Mainly because the mitigation has been around for 3.5 years, and there's a non-zero
chance that making "never" the default could cause hiccups for unsuspecting users.
If this were brand new code, I would definitely opt for "never" as the default.

> If there are concerns about not being able to restart the worker thread, then
> maybe we could make this a .config option?

Eh, a Kconfig is unnecessarily complex, and wouldn't really change anything, e.g.
for users in the know, it's just as easy to force a module param as it is to force
a Kconfig, and to gain any benefit from the param being !never by default, the
Kconfig would also have to be off by default.

If "everyone" wants never to be the default, and Paolo doesn't object, I'd rather
just tack on a patch to make that happen, and cross my fingers there's no fallout :-)