From 20692187eab9fbbcafa4bfd160839278466b65e7 Mon Sep 17 00:00:00 2001 From: Konstantin Belousov Date: Mon, 26 Sep 2016 17:22:44 +0000 Subject: [PATCH] For machines which support PCID but not have INVPCID instruction, i.e. SandyBridge and IvyBridge, correct a race between pmap_activate() and invltlb_pcid_handler(). Reported by and tested by: Slawa Olhovchenkov MFC after: 1 week --- sys/amd64/amd64/pmap.c | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c index 63042e41dd14..59e1b676d00b 100644 --- a/sys/amd64/amd64/pmap.c +++ b/sys/amd64/amd64/pmap.c @@ -6842,6 +6842,7 @@ pmap_activate_sw(struct thread *td) { pmap_t oldpmap, pmap; uint64_t cached, cr3; + register_t rflags; u_int cpuid; oldpmap = PCPU_GET(curpmap); @@ -6865,16 +6866,43 @@ pmap_activate_sw(struct thread *td) pmap == kernel_pmap, ("non-kernel pmap thread %p pmap %p cpu %d pcid %#x", td, pmap, cpuid, pmap->pm_pcids[cpuid].pm_pcid)); + + /* + * If the INVPCID instruction is not available, + * invltlb_pcid_handler() is used for handle + * invalidate_all IPI, which checks for curpmap == + * smp_tlb_pmap. Below operations sequence has a + * window where %CR3 is loaded with the new pmap's + * PML4 address, but curpmap value is not yet updated. + * This causes invltlb IPI handler, called between the + * updates, to execute as NOP, which leaves stale TLB + * entries. + * + * Note that the most typical use of + * pmap_activate_sw(), from the context switch, is + * immune to this race, because interrupts are + * disabled (while the thread lock is owned), and IPI + * happends after curpmap is updated. Protect other + * callers in a similar way, by disabling interrupts + * around the %cr3 register reload and curpmap + * assignment. + */ + if (!invpcid_works) + rflags = intr_disable(); + if (!cached || (cr3 & ~CR3_PCID_MASK) != pmap->pm_cr3) { load_cr3(pmap->pm_cr3 | pmap->pm_pcids[cpuid].pm_pcid | cached); if (cached) PCPU_INC(pm_save_cnt); } + PCPU_SET(curpmap, pmap); + if (!invpcid_works) + intr_restore(rflags); } else if (cr3 != pmap->pm_cr3) { load_cr3(pmap->pm_cr3); + PCPU_SET(curpmap, pmap); } - PCPU_SET(curpmap, pmap); #ifdef SMP CPU_CLR_ATOMIC(cpuid, &oldpmap->pm_active); #else