linux-kernel - Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

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Message-ID: <35bc1f658d1774ad2ea7a38b3874cebff58f7d49.camel@infradead.org>
Date:   Thu, 09 Mar 2023 13:00:36 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        Jörg Rödel <joro@...tes.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
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        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
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        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Subject: Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified
 range to map as encrypted

On Thu, 2023-03-09 at 12:59 +0100, Borislav Petkov wrote:
> 
> So looking at sev_es_init_vc_handling() where we set that key, I'm
> *thinking* that key can be removed now and the code should check
> 
>   cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)
> 
> instead.
> 
> Because if some of the checks in that function below fail, the guest
> will terminate anyway.
> 
> Jörg, Tom?

Hrm... the implication of that is that I should do something like this
in my own code. Is this really your intent?

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index b4265c5b46da..7ac4ec6415de 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1519,24 +1519,17 @@ void __init smp_prepare_cpus_common(void)
  */
 static bool prepare_parallel_bringup(void)
 {
-	bool has_sev_es = sev_es_active();
+	/*
+	 * The "generic" CC_ATTR_GUEST_STATE_ENCRYPT actually means specifically
+	 * SEV-ES, and only SEV-ES, and always shall mean that. If it's present,
+	 * that means the AP startup code should use the hard-coded SEV-ES GHCB
+	 * call to find its APIC ID (STARTUP_APICID_SEV_ES).
+	 */
+	bool has_sev_es = cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT);
 
 	if (IS_ENABLED(CONFIG_X86_32))
 		return false;
 
-	/*
-	 * Encrypted guests other than SEV-ES (in the future) will need to
-	 * implement an early way of finding the APIC ID, since they will
-	 * presumably block direct CPUID too. Be kind to our future selves
-	 * by warning here instead of just letting them break. Parallel
-	 * startup doesn't have to be in the first round of enabling patches
-	 * for any such technology.
-	 */
-	if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT) && !has_sev_es) {
-		pr_info("Disabling parallel bringup due to guest memory encryption\n");
-		return false;
-	}
-
 	if (x2apic_mode || has_sev_es) {
 		if (boot_cpu_data.cpuid_level < 0x0b)
 			return false;


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