[PATCH v10 21/38] x86/fred: No ESPFIX needed when FRED is enabled

[Xin Li <xin3.li@xxxxxxxxx>]

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

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@xxxxxxxxx>
Tested-by: Shan Kang <shan.kang@xxxxxxxxx>
Signed-off-by: Xin Li <xin3.li@xxxxxxxxx>
---
 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 16f9814c9be0..6726e0473d0b 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -106,6 +106,10 @@ void __init init_espfix_bsp(void)
        pgd_t *pgd;
        p4d_t *p4d;
 
+       /* FRED systems always restore the full value of %rsp */
+       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);
@@ -129,6 +133,10 @@ void init_espfix_ap(int cpu)
        void *stack_page;
        pteval_t ptemask;
 
+       /* FRED systems always restore the full value of %rsp */
+       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