linux-kernel - Re: [RFC Part1 PATCH 06/13] x86/compressed: rescinds and validate the memory used for the GHCB

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Message-ID: <20210407111604.GA25319@zn.tnic>
Date:   Wed, 7 Apr 2021 13:16:04 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        ak@...ux.intel.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC Part1 PATCH 06/13] x86/compressed: rescinds and validate
 the memory used for the GHCB

On Tue, Apr 06, 2021 at 10:47:18AM -0500, Brijesh Singh wrote:
> Before the GHCB is established the caller does not need to save and
> restore MSRs. The page_state_change() uses the GHCB MSR protocol and it
> can be called before and after the GHCB is established hence I am saving
> and restoring GHCB MSRs.

I think you need to elaborate on that, maybe with an example. What the
other sites using the GHCB MSR currently do is:

1. request by writing it
2. read the response

None of them save and restore it.

So why here?

Thx.

-- 
Regards/Gruss,
    Boris.

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