linux-kernel - Re: [RFC PATCH V4 10/17] x86/hyperv: Add smp support for sev-snp guest

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <527df1fc-5927-de9c-e18d-00fc1fab575e@gmail.com>
Date:   Sat, 15 Apr 2023 00:22:11 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "jgross@...e.com" <jgross@...e.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "kirill@...temov.name" <kirill@...temov.name>,
        "jiangshan.ljs@...group.com" <jiangshan.ljs@...group.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ashish.kalra@....com" <ashish.kalra@....com>,
        "srutherford@...gle.com" <srutherford@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "anshuman.khandual@....com" <anshuman.khandual@....com>,
        "pawan.kumar.gupta@...ux.intel.com" 
        <pawan.kumar.gupta@...ux.intel.com>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "daniel.sneddon@...ux.intel.com" <daniel.sneddon@...ux.intel.com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "sandipan.das@....com" <sandipan.das@....com>,
        "ray.huang@....com" <ray.huang@....com>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "michael.roth@....com" <michael.roth@....com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "sterritt@...gle.com" <sterritt@...gle.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "samitolvanen@...gle.com" <samitolvanen@...gle.com>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>
Cc:     "pangupta@....com" <pangupta@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH V4 10/17] x86/hyperv: Add smp support for sev-snp
 guest

On 4/12/2023 10:59 PM, Michael Kelley (LINUX) wrote:
>>   #ifdef CONFIG_AMD_MEM_ENCRYPT
>>
>>   #define GHCB_USAGE_HYPERV_CALL	1
>>
>> +static u8 ap_start_input_arg[PAGE_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
>> +static u8 ap_start_stack[PAGE_SIZE] __aligned(PAGE_SIZE);
> Just a question:  ap_start_stack is a static variable that gets used as the
> starting stack for every AP.  So obviously, once each AP is started, we must
> be sure that the AP moves off the ap_start_stack before the next AP is
> started.  How is that synchronization done?  I see that do_boot_cpu() is
> where the wakeup_secondary_cpu() function is called.  Then there's
> some waiting until the AP completes "initial initialization" per the
> comment in the code.  Is there where we know that the AP is no
> longer using ap_start_stack?
> 

Hi Micahel:
	secondary_startup_64_no_verify() in the head_64.S initializes
a boot time stack to replace the old stack. It's very begining stage of
starting AP. The initial_stack was initialized with idle->thread.sp in
the do_boot_cpu(). The AP is started one by one in current code and so
It's safe to reuse the stack for all APs to boot up.

278        /*
279         * Setup a boot time stack - Any secondary CPU will have lost 
its stack
280         * by now because the cr3-switch above unmaps the real-mode stack
281         */
282        movq initial_stack(%rip), %rsp
283