linux-kernel - Re: [PATCH v15 29/41] KVM: SEV: Synchronize MSR_IA32

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Message-ID: <c64a667d9bcb35a7ffee07391b04334f16892305.camel@intel.com>
Date: Thu, 18 Sep 2025 21:42:21 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "john.allen@....com"
	<john.allen@....com>
CC: "Gao, Chao" <chao.gao@...el.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>, "minipli@...ecurity.net"
	<minipli@...ecurity.net>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "mlevitsk@...hat.com"
	<mlevitsk@...hat.com>
Subject: Re: [PATCH v15 29/41] KVM: SEV: Synchronize MSR_IA32_XSS from the
 GHCB when it's valid

On Thu, 2025-09-18 at 16:23 -0500, John Allen wrote:
> The 32bit selftest still doesn't work properly with sev-es, but that was
> a problem with the previous version too. I suspect there's some
> incompatibility between sev-es and the test, but I haven't been able to
> get a good answer on why that might be.

You are talking about test_32bit() in test_shadow_stack.c?

That test relies on a specific CET arch behavior. If you try to transition to a
32 bit compatibility mode segment with an SSP with high bits set (outside the 32
bit address space), a #GP will be triggered by the HW. The test verifies that
this happens and the kernel handles it appropriately. Could it be platform/mode
difference and not KVM issue?