linux-kernel - Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

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Date:   Fri, 8 Dec 2023 17:21:15 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>
Cc:     kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
        linux-mm@...ck.org, linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
        peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
        rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        jarkko@...nel.org, nikunj.dadhania@....com, pankaj.gupta@....com,
        liam.merwick@...cle.com, zhi.a.wang@...el.com,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization
 support

Hello Jeremi,

> Hi Ashish,
> 
> I just noticed that the kernel shouts at me about this bit when I offline->online a CPU in
> an SNP host:

Yes, i also observe the same warning when i bring a CPU back online.
> 
> [2692586.589194] smpboot: CPU 63 is now offline
> [2692589.366822] [Firmware Warn]: MTRR: CPU 0: SYSCFG[MtrrFixDramModEn] not cleared by BIOS, clearing this bit
> [2692589.376582] smpboot: Booting Node 0 Processor 63 APIC 0x3f
> [2692589.378070] [Firmware Warn]: MTRR: CPU 63: SYSCFG[MtrrFixDramModEn] not cleared by BIOS, clearing this bit
> [2692589.388845] microcode: CPU63: new patch_level=0x0a0011d1
> 
> Now I understand if you say "CPU offlining is not supported" but there's nothing currently
> blocking it.
> 

There is CPU hotplug support for SNP platform to do __snp_enable() when 
bringing a CPU back online, but not really sure what needs to be done 
for MtrrFixDramModeEn bit in SYSCFG, discussing with the FW developers.

Thanks,
Ashish