linux-kernel - [PATCH v3 1/2] kvm/cpuid: remove GuestPhysBits code.

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Date: Mon, 11 Mar 2024 11:41:16 +0100
From: Gerd Hoffmann <kraxel@...hat.com>
To: kvm@...r.kernel.org
Cc: Tom Lendacky <thomas.lendacky@....com>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	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 (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT))
Subject: [PATCH v3 1/2] kvm/cpuid: remove GuestPhysBits code.

GuestPhysBits (cpuid leaf 80000008, eax[23:16]) is intended for software
use.  Physical CPUs do not set that field.  The current code which
propagates the host's GuestPhysBits to the guest's PhysBits does not
make sense.  Remove it.

Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
---
 arch/x86/kvm/cpuid.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index adba49afb5fe..c638b5fb2144 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1221,26 +1221,22 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		entry->eax = entry->ebx = entry->ecx = 0;
 		break;
 	case 0x80000008: {
-		unsigned g_phys_as = (entry->eax >> 16) & 0xff;
-		unsigned virt_as = max((entry->eax >> 8) & 0xff, 48U);
-		unsigned phys_as = entry->eax & 0xff;
+		unsigned int virt_as = max((entry->eax >> 8) & 0xff, 48U);
+		unsigned int phys_as;
 
-		/*
-		 * If TDP (NPT) is disabled use the adjusted host MAXPHYADDR as
-		 * the guest operates in the same PA space as the host, i.e.
-		 * reductions in MAXPHYADDR for memory encryption affect shadow
-		 * paging, too.
-		 *
-		 * If TDP is enabled but an explicit guest MAXPHYADDR is not
-		 * provided, use the raw bare metal MAXPHYADDR as reductions to
-		 * the HPAs do not affect GPAs.
-		 */
-		if (!tdp_enabled)
-			g_phys_as = boot_cpu_data.x86_phys_bits;
-		else if (!g_phys_as)
-			g_phys_as = phys_as;
+		if (!tdp_enabled) {
+			/*
+			 * If TDP (NPT) is disabled use the adjusted host
+			 * MAXPHYADDR as the guest operates in the same PA
+			 * space as the host, i.e.  reductions in MAXPHYADDR
+			 * for memory encryption affect shadow paging, too.
+			 */
+			phys_as = boot_cpu_data.x86_phys_bits;
+		} else {
+			phys_as = entry->eax & 0xff;
+		}
 
-		entry->eax = g_phys_as | (virt_as << 8);
+		entry->eax = phys_as | (virt_as << 8);
 		entry->ecx &= ~(GENMASK(31, 16) | GENMASK(11, 8));
 		entry->edx = 0;
 		cpuid_entry_override(entry, CPUID_8000_0008_EBX);
-- 
2.44.0