linux-kernel - Re: [PATCH v13 17/22] x86/kexec: Flush cache of TDX private memory

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Date:   Fri, 15 Sep 2023 17:43:27 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Huang, Kai" <kai.huang@...el.com>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v13 17/22] x86/kexec: Flush cache of TDX private memory

On Sat, 2023-08-26 at 00:14 +1200, Kai Huang wrote:
> There are two problems in terms of using kexec() to boot to a new
> kernel
> when the old kernel has enabled TDX: 1) Part of the memory pages are
> still TDX private pages; 2) There might be dirty cachelines
> associated
> with TDX private pages.

Does TDX support hibernate? I'm wondering about two potential problems:
1. Reading/writing private pages from the direct map on save/restore
2. The seam module needing to be re-inited (the tdx_enable() stuff)

If that's the case you could have something like the below to just
block it when TDX could be in use:
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 2b4a946a6ff5..3b1b7202452d 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -84,7 +84,8 @@ bool hibernation_available(void)
 {
        return nohibernate == 0 &&
                !security_locked_down(LOCKDOWN_HIBERNATION) &&
-               !secretmem_active() && !cxl_mem_active();
+               !secretmem_active() && !cxl_mem_active() &&
+               !platform_tdx_enabled();
 }
 
 /**

Or maybe better, it could check tdx_module_status? But there is no way
to read that variable from hibernate.