linux-kernel - [PATCH] x86/tdx: Allow extended topology CPUID leafs to be emulated by hypercall

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Message-ID: <20230908175644.2478924-1-sagis@google.com>
Date:   Fri,  8 Sep 2023 10:56:44 -0700
From:   Sagi Shahar <sagis@...gle.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Vishal Annapurve <vannapurve@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Nikolay Borisov <nik.borisov@...e.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Sagi Shahar <sagis@...gle.com>
Subject: [PATCH] x86/tdx: Allow extended topology CPUID leafs to be emulated
 by hypercall

The current TDX module does not handle extended topology leaves
explicitly and will generate a #VE but the current #VE handler
implementation blindly returns 0 for those CPUID leaves.

This currently causes TDX guests to see 0 values when querying the numa
topology leading to incorrect numa configurations.

This patch fixes this behavior by emulating the extended topology leaves
using the CPUID hypercall.

Change-Id: I427807e3ac8d9e3be50a6fac40ebd3f54b445b0c
Signed-off-by: Sagi Shahar <sagis@...gle.com>
---
 arch/x86/coco/tdx/tdx.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 1d6b863c42b0..db9a4673555a 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -321,13 +321,16 @@ static int handle_cpuid(struct pt_regs *regs, struct ve_info *ve)
 	};
 
 	/*
-	 * Only allow VMM to control range reserved for hypervisor
-	 * communication.
+	 * Only emulate CPUID in 2 cases:
+	 * - CPUID is in the range reserved for hypervisor communication.
+	 * - CPUID is an extended topology leaf which is not emulated natively
+	 *   by the TDX module.
 	 *
-	 * Return all-zeros for any CPUID outside the range. It matches CPU
-	 * behaviour for non-supported leaf.
+	 * Return all-zeros for any other CPUID. It matches CPU behaviour for
+	 * non-supported leaf.
 	 */
-	if (regs->ax < 0x40000000 || regs->ax > 0x4FFFFFFF) {
+	if ((regs->ax < 0x40000000 || regs->ax > 0x4FFFFFFF) &&
+	    regs->ax != 0x0b && regs->ax != 0x1f) {
 		regs->ax = regs->bx = regs->cx = regs->dx = 0;
 		return ve_instr_len(ve);
 	}
-- 
2.42.0.283.g2d96d420d3-goog