[PATCH] Proper fix for highmem kmap_atomic functions for VMI for 2.6.21

Since lazy MMU batching mode still allows interrupts to enter, it is
possible for interrupt handlers to try to use kmap_atomic, which fails when
lazy mode is active, since the PTE update to highmem will be delayed.  The
best workaround is to issue an explicit flush in kmap_atomic_functions
case; this is the only way nested PTE updates can happen in the interrupt
handler.

Thanks to Jeremy Fitzhardinge for noting the bug and suggestions on a fix.

This patch gets reverted again when we start 2.6.22 and the bug gets fixed
differently.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 1 deletions

diff --git a/arch/i386/kernel/vmi.c b/arch/i386/kernel/vmi.c
index fb07a1aad225..edc339fa5038 100644
--- a/arch/i386/kernel/vmi.c
+++ b/arch/i386/kernel/vmi.c
@@ -69,6 +69,7 @@ struct {
 	void (*flush_tlb)(int);
 	void (*set_initial_ap_state)(int, int);
 	void (*halt)(void);
+  	void (*set_lazy_mode)(int mode);
 } vmi_ops;
 
 /* XXX move this to alternative.h */
@@ -574,6 +575,26 @@ vmi_startup_ipi_hook(int phys_apicid, unsigned long start_eip,
 }
 #endif
 
+static void vmi_set_lazy_mode(int mode)
+{
+	static DEFINE_PER_CPU(int, lazy_mode);
+
+	if (!vmi_ops.set_lazy_mode)
+		return;
+
+	/* Modes should never nest or overlap */
+	BUG_ON(__get_cpu_var(lazy_mode) && !(mode == PARAVIRT_LAZY_NONE ||
+					     mode == PARAVIRT_LAZY_FLUSH));
+
+	if (mode == PARAVIRT_LAZY_FLUSH) {
+		vmi_ops.set_lazy_mode(0);
+		vmi_ops.set_lazy_mode(__get_cpu_var(lazy_mode));
+	} else {
+		vmi_ops.set_lazy_mode(mode);
+		__get_cpu_var(lazy_mode) = mode;
+	}
+}
+
 static inline int __init check_vmi_rom(struct vrom_header *rom)
 {
 	struct pci_header *pci;
@@ -804,7 +825,7 @@ static inline int __init activate_vmi(void)
 	para_wrap(load_esp0, vmi_load_esp0, set_kernel_stack, UpdateKernelStack);
 	para_fill(set_iopl_mask, SetIOPLMask);
 	para_fill(io_delay, IODelay);
-	para_fill(set_lazy_mode, SetLazyMode);
+	para_wrap(set_lazy_mode, vmi_set_lazy_mode, set_lazy_mode, SetLazyMode);
 
 	/* user and kernel flush are just handled with different flags to FlushTLB */
 	para_wrap(flush_tlb_user, vmi_flush_tlb_user, flush_tlb, FlushTLB);