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Subject[RFC PATCH 26/32] x86/fred: no ESPFIX needed when FRED is enabled
Date
From: "H. Peter Anvin (Intel)" <hpa@zytor.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@zytor.com>
Signed-off-by: Xin Li <xin3.li@intel.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
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