linux-kernel - [PATCH] KVM: pass through CPUID 0x80000005

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Message-ID: <20230712183136.85561-1-itazur@amazon.com>
Date:   Wed, 12 Jul 2023 19:31:36 +0100
From:   Takahiro Itazuri <itazur@...zon.com>
To:     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>,
        "H . Peter Anvin" <hpa@...or.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Takahiro Itazuri <zulinx86@...il.com>,
        Takahiro Itazuri <itazur@...zon.com>
Subject: [PATCH] KVM: pass through CPUID 0x80000005

Pass CPUID 0x80000005 (L1 cache and TLB info).

CPUID 0x80000006 (L2 cache and TLB and L3 cache info) has been returned
since commit 43d05de2bee7 ("KVM: pass through CPUID(0x80000006)").
Enumerating both 0x80000005 and 0x80000006 with KVM_GET_SUPPORTED_CPUID
would be better than reporting either, and 0x80000005 could be helpful
for VMM to pass it to KVM_SET_CPUID{,2} for the same reason with
0x80000006..

Signed-off-by: Takahiro Itazuri <itazur@...zon.com>
---

Discussion was made a bit on
https://lore.kernel.org/all/20230712170258.75355-1-itazur@amazon.com/.
If there is any reason that leaf 0x80000005 should not be enumerated or
dropping leaf 0x80000006 is preferred, please feel free to share your
thoughts.

---
 arch/x86/kvm/cpuid.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0c9660a07b23..54a5b256c484 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1152,6 +1152,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		cpuid_entry_override(entry, CPUID_8000_0001_EDX);
 		cpuid_entry_override(entry, CPUID_8000_0001_ECX);
 		break;
+	case 0x80000005:
+		/*  Pass host L1 cache and TLB info. */
+		break;
 	case 0x80000006:
 		/* Drop reserved bits, pass host L2 cache and TLB info. */
 		entry->edx &= ~GENMASK(17, 16);
-- 
2.38.0