linux-kernel - [PATCH v9 06/22] x86/cea: Export __this_cpu_ist_top

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Message-ID: <20251026201911.505204-7-xin@zytor.com>
Date: Sun, 26 Oct 2025 13:18:54 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org
Cc: pbonzini@...hat.com, seanjc@...gle.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, xin@...or.com, luto@...nel.org,
        peterz@...radead.org, andrew.cooper3@...rix.com, chao.gao@...el.com,
        hch@...radead.org, sohil.mehta@...el.com
Subject: [PATCH v9 06/22] x86/cea: Export __this_cpu_ist_top_va() to KVM

Export __this_cpu_ist_top_va() to allow KVM to retrieve the per-CPU
exception stack top.

FRED introduced new fields in the host-state area of the VMCS for stack
levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively corresponding to
per-CPU exception stacks for #DB, NMI and #DF.  KVM must populate these
fields each time a vCPU is loaded onto a CPU.

Signed-off-by: Xin Li (Intel) <xin@...or.com>
---
 arch/x86/mm/cpu_entry_area.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index b3d90f9cfbb1..e507621d5c20 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -19,6 +19,11 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(struct exception_stacks, exception_stacks);
 DEFINE_PER_CPU(struct cea_exception_stacks*, cea_exception_stacks);
 
 /*
+ * FRED introduced new fields in the host-state area of the VMCS for
+ * stack levels 1->3 (HOST_IA32_FRED_RSP[123]), each respectively
+ * corresponding to per CPU stacks for #DB, NMI and #DF.  KVM must
+ * populate these each time a vCPU is loaded onto a CPU.
+ *
  * Typically invoked by entry code, so must be noinstr.
  */
 noinstr unsigned long __this_cpu_ist_bottom_va(enum exception_stack_ordering stack)
@@ -36,6 +41,7 @@ noinstr unsigned long __this_cpu_ist_top_va(enum exception_stack_ordering stack)
 {
 	return __this_cpu_ist_bottom_va(stack) + EXCEPTION_STKSZ;
 }
+EXPORT_SYMBOL_FOR_MODULES(__this_cpu_ist_top_va, "kvm-intel");
 
 static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, _cea_offset);
 
-- 
2.51.0