linux-kernel - [RFC PATCH 26/32] x86/fred: no ESPFIX needed when FRED is enabled

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Date:   Mon, 19 Dec 2022 22:36:52 -0800
From:   Xin Li <xin3.li@...el.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, peterz@...radead.org,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: [RFC PATCH 26/32] x86/fred: no ESPFIX needed when FRED is enabled

From: "H. Peter Anvin (Intel)" <hpa@...or.com>

Because FRED always restores the full value of %rsp, ESPFIX is
no longer needed when it's enabled.

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
Signed-off-by: Xin Li <xin3.li@...el.com>
---
 arch/x86/kernel/espfix_64.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 9417d5aa7305..b594fcc0a4b7 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -116,6 +116,10 @@ void __init init_espfix_bsp(void)
 	pgd_t *pgd;
 	p4d_t *p4d;
 
+	/* FRED systems don't need ESPFIX */
+	if (cpu_feature_enabled(X86_FEATURE_FRED))
+		return;
+
 	/* Install the espfix pud into the kernel page directory */
 	pgd = &init_top_pgt[pgd_index(ESPFIX_BASE_ADDR)];
 	p4d = p4d_alloc(&init_mm, pgd, ESPFIX_BASE_ADDR);
@@ -139,6 +143,10 @@ void init_espfix_ap(int cpu)
 	void *stack_page;
 	pteval_t ptemask;
 
+	/* FRED systems don't need ESPFIX */
+	if (cpu_feature_enabled(X86_FEATURE_FRED))
+		return;
+
 	/* We only have to do this once... */
 	if (likely(per_cpu(espfix_stack, cpu)))
 		return;		/* Already initialized */
-- 
2.34.1