linux-kernel - [PATCH] KVM: x86/mmu: Warn on nx_huge

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Message-Id: <20211019121848.245347-1-liyu.yukiteru@bytedance.com>
Date:   Tue, 19 Oct 2021 20:18:48 +0800
From:   Li Yu <liyu.yukiteru@...edance.com>
To:     pbonzini@...hat.com
Cc:     liyu.yukiteru@...edance.com,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: x86/mmu: Warn on nx_huge_pages when initializing kvm

Add warning when `nx_huge_pages` is enabled by kvm mmu for hint that
huge pages may be splited by kernel.

Signed-off-by: Li Yu <liyu.yukiteru@...edance.com>
---
 arch/x86/kvm/mmu/mmu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 1a64ba5b9437..b75dbaf29f2d 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6091,12 +6091,17 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp)
 	return 0;
 }
 
+#define ITLB_MULTIHIT_MSG "iTLB multi-hit CPU bug present and cpu mitigations enabled, huge pages may be splited by kernel for security. See CVE-2018-12207 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/multihit.html for details.\n"
+
 int kvm_mmu_module_init(void)
 {
 	int ret = -ENOMEM;
 
-	if (nx_huge_pages == -1)
+	if (nx_huge_pages == -1) {
 		__set_nx_huge_pages(get_nx_auto_mode());
+		if (is_nx_huge_page_enabled())
+			pr_warn_once(ITLB_MULTIHIT_MSG);
+	}
 
 	/*
 	 * MMU roles use union aliasing which is, generally speaking, an
-- 
2.11.0