[PATCH] x86/flushtlb: remove flush_area check on system state

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Booting with Shadow Stacks leads to the following assert on a debug
hypervisor:

(XEN) [   11.625166] Assertion 'local_irq_is_enabled()' failed at 
arch/x86/smp.c:265
(XEN) [   11.629410] ----[ Xen-4.17.0-10.24-d  x86_64  debug=y  Not tainted 
]----
(XEN) [   11.633679] CPU:    0
(XEN) [   11.637834] RIP:    e008:[<ffff82d040345300>] 
flush_area_mask+0x40/0x13e
[...]
(XEN) [   11.806158] Xen call trace:
(XEN) [   11.811255]    [<ffff82d040345300>] R flush_area_mask+0x40/0x13e
(XEN) [   11.816459]    [<ffff82d040338a40>] F modify_xen_mappings+0xc5/0x958
(XEN) [   11.821689]    [<ffff82d0404474f9>] F 
arch/x86/alternative.c#_alternative_instructions+0xb7/0xb9
(XEN) [   11.827053]    [<ffff82d0404476cc>] F alternative_branches+0xf/0x12
(XEN) [   11.832416]    [<ffff82d04044e37d>] F __start_xen+0x1ef4/0x2776
(XEN) [   11.837809]    [<ffff82d040203344>] F __high_start+0x94/0xa0


This is due to SYS_STATE_smp_boot being set before calling
alternative_branches(), and the flush in modify_xen_mappings() then
using flush_area_all() with interrupts disabled.  Note that
alternative_branches() is called before APs are started, so the flush
must be a local one (and indeed the cpumask passed to
flush_area_mask() just contains one CPU).

Take the opportunity to simplify a bit the logic and make flush_area()
an alias for flush_area_mask(&cpu_online_map...), taking into account
that cpu_online_map just contains the BSP before APs are started.
This requires widening the assert in flush_area_mask() to allow
being called with interrupts disabled as long as it's strictly a local
only flush.

The overall result is that a conditional can be removed from
flush_area().

Fixes: (78e072bc37 'x86/mm: avoid inadvertently degrading a TLB flush to local 
only')
Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/include/asm/flushtlb.h | 3 ++-
 xen/arch/x86/mm.c                   | 8 --------
 xen/arch/x86/smp.c                  | 3 ++-
 3 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/include/asm/flushtlb.h 
b/xen/arch/x86/include/asm/flushtlb.h
index 18777f1d4c..a97b3a2327 100644
--- a/xen/arch/x86/include/asm/flushtlb.h
+++ b/xen/arch/x86/include/asm/flushtlb.h
@@ -146,7 +146,8 @@ void flush_area_mask(const cpumask_t *, const void *va, 
unsigned int flags);
 #define flush_mask(mask, flags) flush_area_mask(mask, NULL, flags)
 
 /* Flush all CPUs' TLBs/caches */
-#define flush_area_all(va, flags) flush_area_mask(&cpu_online_map, va, flags)
+#define flush_area(va, flags) \
+    flush_area_mask(&cpu_online_map, (const void *)(va), flags)
 #define flush_all(flags) flush_mask(&cpu_online_map, flags)
 
 /* Flush local TLBs */
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 67c0427963..45235c5aa6 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5066,14 +5066,6 @@ l1_pgentry_t *virt_to_xen_l1e(unsigned long v)
 #define l1f_to_lNf(f) (((f) & _PAGE_PRESENT) ? ((f) |  _PAGE_PSE) : (f))
 #define lNf_to_l1f(f) (((f) & _PAGE_PRESENT) ? ((f) & ~_PAGE_PSE) : (f))
 
-/*
- * map_pages_to_xen() can be called early in boot before any other
- * CPUs are online. Use flush_area_local() in this case.
- */
-#define flush_area(v,f) (system_state < SYS_STATE_smp_boot ?    \
-                         flush_area_local((const void *)v, f) : \
-                         flush_area_all((const void *)v, f))
-
 #define L3T_INIT(page) (page) = ZERO_BLOCK_PTR
 
 #define L3T_LOCK(page)        \
diff --git a/xen/arch/x86/smp.c b/xen/arch/x86/smp.c
index 0a02086966..2f4e98cec9 100644
--- a/xen/arch/x86/smp.c
+++ b/xen/arch/x86/smp.c
@@ -262,7 +262,8 @@ void flush_area_mask(const cpumask_t *mask, const void *va, 
unsigned int flags)
 {
     unsigned int cpu = smp_processor_id();
 
-    ASSERT(local_irq_is_enabled());
+    /* Local flushes can be performed with interrupts disabled. */
+    ASSERT(local_irq_is_enabled() || cpumask_equal(mask, cpumask_of(cpu)));
 
     if ( (flags & ~(FLUSH_VCPU_STATE | FLUSH_ORDER_MASK)) &&
          cpumask_test_cpu(cpu, mask) )
-- 
2.36.0