linux-kernel - [PATCH RESEND 2/2] KVM: SVM: add some info prints to SEV init

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Date:   Thu, 20 Apr 2023 10:47:17 +0200
From:   Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To:     pbonzini@...hat.com
Cc:     Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH RESEND 2/2] KVM: SVM: add some info prints to SEV init

Let's add a few pr_info's to sev_hardware_setup to make SEV/SEV-ES
enabling a little bit handier for users. Right now it's too hard
to guess why SEV/SEV-ES are failing to enable.

There are a few reasons.
SEV:
- NPT is disabled (module parameter)
- CPU lacks some features (sev, decodeassists)
- Maximum SEV ASID is 0

SEV-ES:
- mmio_caching is disabled (module parameter)
- CPU lacks sev_es feature
- Minimum SEV ASID value is 1 (can be adjusted in BIOS/UEFI)

Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Stéphane Graber <stgraber@...ntu.com>
Cc: kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
---
 arch/x86/kvm/svm/sev.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index a42536a0681a..14cbb8f14c6b 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2168,17 +2168,24 @@ void __init sev_hardware_setup(void)
 	bool sev_es_supported = false;
 	bool sev_supported = false;
 
-	if (!sev_enabled || !npt_enabled)
+	if (!sev_enabled)
 		goto out;
 
+	if (!npt_enabled) {
+		pr_info("Failed to enable AMD SEV as it requires Nested Paging to be enabled\n");
+		goto out;
+	}
+
 	/*
 	 * SEV must obviously be supported in hardware.  Sanity check that the
 	 * CPU supports decode assists, which is mandatory for SEV guests to
 	 * support instruction emulation.
 	 */
 	if (!boot_cpu_has(X86_FEATURE_SEV) ||
-	    WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)))
+	    WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS))) {
+		pr_info("Failed to enable AMD SEV as it requires decodeassists and sev CPU features\n");
 		goto out;
+	}
 
 	/* Retrieve SEV CPUID information */
 	cpuid(0x8000001f, &eax, &ebx, &ecx, &edx);
@@ -2188,8 +2195,10 @@ void __init sev_hardware_setup(void)
 
 	/* Maximum number of encrypted guests supported simultaneously */
 	max_sev_asid = ecx;
-	if (!max_sev_asid)
+	if (!max_sev_asid) {
+		pr_info("Failed to enable SEV as the maximum SEV ASID value is 0.\n");
 		goto out;
+	}
 
 	/* Minimum ASID value that should be used for SEV guest */
 	min_sev_asid = edx;
@@ -2234,16 +2243,22 @@ void __init sev_hardware_setup(void)
 	 * instead relies on #NPF(RSVD) being reflected into the guest as #VC
 	 * (the guest can then do a #VMGEXIT to request MMIO emulation).
 	 */
-	if (!enable_mmio_caching)
+	if (!enable_mmio_caching) {
+		pr_info("Failed to enable SEV-ES as it requires MMIO caching to be enabled\n");
 		goto out;
+	}
 
 	/* Does the CPU support SEV-ES? */
-	if (!boot_cpu_has(X86_FEATURE_SEV_ES))
+	if (!boot_cpu_has(X86_FEATURE_SEV_ES)) {
+		pr_info("Failed to enable SEV-ES as it requires sev_es CPU feature\n");
 		goto out;
+	}
 
 	/* Has the system been allocated ASIDs for SEV-ES? */
-	if (min_sev_asid == 1)
+	if (min_sev_asid == 1) {
+		pr_info("Failed to enable SEV-ES as the minimum SEV ASID value is 1.\n");
 		goto out;
+	}
 
 	sev_es_asid_count = min_sev_asid - 1;
 	if (misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count))
-- 
2.34.1