Ensure that a thread stays on same CPU when calculating per CPU

TLB shootdown requirements. Otherwise a CPU may not get the needed
TLB invalidation.

The PTE valid and access flags can not be used here to avoid TLB
shootdowns unless sf->cpumask == all_cpus.
( Otherwise some CPUs may still hold an even older entry in the TLB)
Since sf_buf_alloc mappings are normally always used this is
also not really useful and presetting accessed and modified
allows the CPU to speculatively load the entry into the TLB.

Both bugs can cause random data corruption.

MFC after:	3 days

1 files changed, 15 insertions, 15 deletions

diff --git a/sys/i386/i386/vm_machdep.c b/sys/i386/i386/vm_machdep.c
index 1cec91b..ce2ea83 100644
--- a/sys/i386/i386/vm_machdep.c
+++ b/sys/i386/i386/vm_machdep.c
@@ -63,6 +63,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/proc.h>
 #include <sys/sf_buf.h>
 #include <sys/smp.h>
+#include <sys/sched.h>
 #include <sys/sysctl.h>
 #include <sys/unistd.h>
 #include <sys/vnode.h>
@@ -672,6 +673,7 @@ sf_buf_alloc(struct vm_page *m, int flags)
 				nsfbufspeak = imax(nsfbufspeak, nsfbufsused);
 			}
 #ifdef SMP
+			sched_pin();
 			cpumask = PCPU_GET(cpumask);
 			if ((sf->cpumask & cpumask) == 0) {
 				sf->cpumask |= cpumask;
@@ -686,6 +688,8 @@ sf_buf_alloc(struct vm_page *m, int flags)
 					mtx_unlock_spin(&smp_ipi_mtx);
 				}
 			}
+			sched_unpin();
+		
 #endif
 			goto done;
 		}
@@ -716,28 +720,24 @@ sf_buf_alloc(struct vm_page *m, int flags)
 
 	/*
 	 * Update the sf_buf's virtual-to-physical mapping, flushing the
-	 * virtual address from the TLB only if the PTE implies that the old
-	 * mapping has been used.  Since the reference count for the sf_buf's
-	 * old mapping was zero, that mapping is not currently in use.
-	 * Consequently, there is no need to exchange the old and new PTEs
-	 * atomically, even under PAE.
+	 * virtual address from the TLB. Since the reference count for 
+	 * the sf_buf's old mapping was zero, that mapping is not 
+	 * currently in use. Consequently, there is no need to exchange 
+	 * the old and new PTEs atomically, even under PAE.
 	 */
 	ptep = vtopte(sf->kva);
 	opte = *ptep;
-	*ptep = VM_PAGE_TO_PHYS(m) | pgeflag | PG_RW | PG_V;
+	*ptep = VM_PAGE_TO_PHYS(m) | pgeflag | PG_RW | PG_V | PG_A | PG_M;
 #ifdef SMP
 	if (flags & SFB_CPUPRIVATE) {
-		if ((opte & (PG_A | PG_V)) == (PG_A | PG_V)) {
-			sf->cpumask = PCPU_GET(cpumask);
-			invlpg(sf->kva);
-		} else
-			sf->cpumask = all_cpus;
+		sf->cpumask = PCPU_GET(cpumask);
+		invlpg(sf->kva);
 		goto done;
-	} else
-		sf->cpumask = all_cpus;
+	}
+       
+	sf->cpumask = all_cpus;
 #endif
-	if ((opte & (PG_A | PG_V)) == (PG_A | PG_V))
-		pmap_invalidate_page(kernel_pmap, sf->kva);
+	pmap_invalidate_page(kernel_pmap, sf->kva);
 done:
 	mtx_unlock(&sf_buf_lock);
 	return (sf);