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From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 14 Jun 2022 23:15:52 +0200
Subject: x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value
Origin: https://git.kernel.org/linus/caa0ff24d5d0e02abce5e65c3d2b7f20a6617be5
Due to TIF_SSBD and TIF_SPEC_IB the actual IA32_SPEC_CTRL value can
differ from x86_spec_ctrl_base. As such, keep a per-CPU value
reflecting the current task's MSR content.
[jpoimboe: rename]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/nospec-branch.h | 1 +
arch/x86/kernel/cpu/bugs.c | 28 +++++++++++++++++++++++-----
arch/x86/kernel/process.c | 2 +-
3 files changed, 25 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 5ca60ae0d14f..bac243da5130 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -253,6 +253,7 @@ static inline void indirect_branch_prediction_barrier(void)
/* The Intel SPEC CTRL MSR base value cache */
extern u64 x86_spec_ctrl_base;
+extern void write_spec_ctrl_current(u64 val);
/*
* With retpoline, we must use IBRS to restrict branch prediction
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fb249b2c1eb0..ce7435593c3e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -49,11 +49,29 @@ static void __init mmio_select_mitigation(void);
static void __init srbds_select_mitigation(void);
static void __init l1d_flush_select_mitigation(void);
-/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
+/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
+
+/* The current value of the SPEC_CTRL MSR with task-specific bits set */
+DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
+EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
+
static DEFINE_MUTEX(spec_ctrl_mutex);
+/*
+ * Keep track of the SPEC_CTRL MSR value for the current task, which may differ
+ * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update().
+ */
+void write_spec_ctrl_current(u64 val)
+{
+ if (this_cpu_read(x86_spec_ctrl_current) == val)
+ return;
+
+ this_cpu_write(x86_spec_ctrl_current, val);
+ wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
/*
* The vendor and possibly platform specific bits which can be modified in
* x86_spec_ctrl_base.
@@ -1279,7 +1297,7 @@ static void __init spectre_v2_select_mitigation(void)
if (spectre_v2_in_eibrs_mode(mode)) {
/* Force it so VMEXIT will restore correctly */
x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
}
switch (mode) {
@@ -1334,7 +1352,7 @@ static void __init spectre_v2_select_mitigation(void)
static void update_stibp_msr(void * __unused)
{
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
}
/* Update x86_spec_ctrl_base in case SMT state changed. */
@@ -1577,7 +1595,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
x86_amd_ssb_disable();
} else {
x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
}
}
@@ -1828,7 +1846,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
void x86_spec_ctrl_setup_ap(void)
{
if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
- wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+ write_spec_ctrl_current(x86_spec_ctrl_base);
if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
x86_amd_ssb_disable();
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9b2772b7e1f3..05611f66d013 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -600,7 +600,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
}
if (updmsr)
- wrmsrl(MSR_IA32_SPEC_CTRL, msr);
+ write_spec_ctrl_current(msr);
}
static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
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