Kernel TLB invalidation IPIs are a common source of interference on
NOHZ_FULL CPUs. Given NOHZ_FULL CPUs executing in userspace are not
accessing any kernel addresses, these invalidations do not need to happen
immediately, and can be deferred until the next user->kernel transition.
Rather than make __flush_tlb_all() noinstr, add a minimal noinstr
variant that doesn't try to leverage INVPCID.
FIXME: not fully noinstr compliant
XXX: same issue as with ins patching, when do we access data that should be
invalidated?
Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx>
---
arch/x86/include/asm/context_tracking_work.h | 4 ++++
arch/x86/include/asm/tlbflush.h | 1 +
arch/x86/mm/tlb.c | 17 +++++++++++++++++
include/linux/context_tracking_work.h | 2 ++
4 files changed, 24 insertions(+)
diff --git a/arch/x86/include/asm/context_tracking_work.h b/arch/x86/include/asm/context_tracking_work.h
index 2c66687ce00e2..9d4f021b5a45b 100644
--- a/arch/x86/include/asm/context_tracking_work.h
+++ b/arch/x86/include/asm/context_tracking_work.h
@@ -3,6 +3,7 @@
#define _ASM_X86_CONTEXT_TRACKING_WORK_H
#include <asm/sync_core.h>
+#include <asm/tlbflush.h>
static __always_inline void arch_context_tracking_work(int work)
{
@@ -10,6 +11,9 @@ static __always_inline void arch_context_tracking_work(int work)
case CONTEXT_WORK_SYNC:
sync_core();
break;
+ case CONTEXT_WORK_TLBI:
+ __flush_tlb_all_noinstr();
+ break;
}
}
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 75bfaa4210303..9064aa0027d05 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -15,6 +15,7 @@
#include <asm/pgtable.h>
void __flush_tlb_all(void);
+void noinstr __flush_tlb_all_noinstr(void);
#define TLB_FLUSH_ALL -1UL
#define TLB_GENERATION_INVALID 0
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 267acf27480af..631df9189ded4 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1237,6 +1237,23 @@ void __flush_tlb_all(void)
}
EXPORT_SYMBOL_GPL(__flush_tlb_all);
+void noinstr __flush_tlb_all_noinstr(void)
+{
+ /*
+ * This is for invocation in early entry code that cannot be
+ * instrumented. A RMW to CR4 works for most cases, but relies on
+ * being able to flip either of the PGE or PCIDE bits. Flipping CR4.PCID
+ * would require also resetting CR3.PCID, so just try with CR4.PGE, else
+ * do the CR3 write.
+ *
+ * TODO: paravirt
+ */
+ if (cpu_feature_enabled(X86_FEATURE_PGE))
+ __native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
+ else
+ flush_tlb_local();
+}
+
void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
{
struct flush_tlb_info *info;
diff --git a/include/linux/context_tracking_work.h b/include/linux/context_tracking_work.h
index b0c7463048b60..c084a60d2fec5 100644
--- a/include/linux/context_tracking_work.h
+++ b/include/linux/context_tracking_work.h
@@ -7,12 +7,14 @@
enum {
CONTEXT_WORK_DISABLED_OFFSET,
CONTEXT_WORK_SYNC_OFFSET,
+ CONTEXT_WORK_TLBI_OFFSET,
CONTEXT_WORK_MAX_OFFSET
};
enum ct_work {
CONTEXT_WORK_DISABLED = BIT(CONTEXT_WORK_DISABLED_OFFSET),
CONTEXT_WORK_SYNC = BIT(CONTEXT_WORK_SYNC_OFFSET),
+ CONTEXT_WORK_TLBI = BIT(CONTEXT_WORK_TLBI_OFFSET),
CONTEXT_WORK_MAX = BIT(CONTEXT_WORK_MAX_OFFSET)
};
--
2.31.1
