linux-kernel - Re: [patch] x86/smpboot: Disable parallel bootup if cc

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Date:   Tue, 30 May 2023 18:00:46 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        David Woodhouse <dwmw2@...radead.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Paul McKenney <paulmck@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Usama Arif <usama.arif@...edance.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        linux-csky@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Sabin Rapan <sabrapan@...zon.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [patch] x86/smpboot: Disable parallel bootup if cc_vendor != NONE

On Tue, May 30 2023 at 15:29, Kirill A. Shutemov wrote:
> On Tue, May 30, 2023 at 02:09:17PM +0200, Thomas Gleixner wrote:
>> The decision to allow parallel bringup of secondary CPUs checks
>> CC_ATTR_GUEST_STATE_ENCRYPT to detect encrypted guests. Those cannot use
>> parallel bootup because accessing the local APIC is intercepted and raises
>> a #VC or #VE, which cannot be handled at that point.
>> 
>> The check works correctly, but only for AMD encrypted guests. TDX does not
>> set that flag.
>> 
>> Check for cc_vendor != CC_VENDOR_NONE instead. That might be overbroad, but
>> definitely works for both AMD and Intel.
>
> It boots fine with TDX, but I think it is wrong. cc_get_vendor() will
> report CC_VENDOR_AMD even on bare metal if SME is enabled. I don't think
> we want it.

Right. Did not think about that.

But the same way is CC_ATTR_GUEST_MEM_ENCRYPT overbroad for AMD. Only
SEV-ES traps RDMSR if I'm understandig that maze correctly.

Thanks,

        tglx