We can use PCID if the CPU has PCID and PGE and we're not on Xen.
By itself, this has no effect. The next patch will start using
PCID.
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
arch/x86/include/asm/tlbflush.h | 8 ++++++++
arch/x86/kernel/cpu/common.c | 15 +++++++++++++++
arch/x86/xen/enlighten_pv.c | 6 ++++++
3 files changed, 29 insertions(+)
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 87b13e51e867..57b305e13c4c 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -243,6 +243,14 @@ static inline void __flush_tlb_all(void)
__flush_tlb_global();
else
__flush_tlb();
+
+ /*
+ * Note: if we somehow had PCID but not PGE, then this wouldn't work --
+ * we'd end up flushing kernel translations for the current ASID but
+ * we might fail to flush kernel translations for other cached ASIDs.
+ *
+ * To avoid this issue, we force PCID off if PGE is off.
+ */
}
static inline void __flush_tlb_one(unsigned long addr)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 904485e7b230..01caf66b270f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1143,6 +1143,21 @@ static void identify_cpu(struct cpuinfo_x86 *c)
setup_smep(c);
setup_smap(c);
+ /* Set up PCID */
+ if (cpu_has(c, X86_FEATURE_PCID)) {
+ if (cpu_has(c, X86_FEATURE_PGE)) {
+ cr4_set_bits(X86_CR4_PCIDE);
+ } else {
+ /*
+ * flush_tlb_all(), as currently implemented, won't
+ * work if PCID is on but PGE is not. Since that
+ * combination doesn't exist on real hardware, there's
+ * no reason to try to fully support it.
+ */
+ clear_cpu_cap(c, X86_FEATURE_PCID);
+ }
+ }
+
/*
* The vendor-specific functions might have changed features.
* Now we do "generic changes."
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index f33eef4ebd12..a136aac543c3 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -295,6 +295,12 @@ static void __init xen_init_capabilities(void)
setup_clear_cpu_cap(X86_FEATURE_ACC);
setup_clear_cpu_cap(X86_FEATURE_X2APIC);
+ /*
+ * Xen PV would need some work to support PCID: CR3 handling as well
+ * as xen_flush_tlb_others() would need updating.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_PCID);
+
if (!xen_initial_domain())
setup_clear_cpu_cap(X86_FEATURE_ACPI);
--
2.9.4
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