[Xen-devel] [PATCH] hvm/hpet: Correctly gate the virtual HPET on HVM_PARAM_HPET_ENABLE

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s 3f8e22de7 "x86 hvm: Allow HPET to be configured as a per-domain config
option" introduced the parameter to conditionally enable the HPET.

However, having the check in hpet_range() does not have the intended effect.
As currently implemented, when the HPET is disabled, the range is not claimed
and an ioreq is forwarded to qemu, which implements an HPET itself.

Properly disable the HPET by always claiming the range, dropping writes and
reading ~0.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>

---

This patch has been in XenServer for a couple of releases now, although
disabling the HPET is not a common action to take and is only really useful
for debugging purposes.
---
 xen/arch/x86/hvm/hpet.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/hpet.c b/xen/arch/x86/hvm/hpet.c
index bdfc6fc..d898169 100644
--- a/xen/arch/x86/hvm/hpet.c
+++ b/xen/arch/x86/hvm/hpet.c
@@ -173,6 +173,12 @@ static int hpet_read(
     unsigned long result;
     uint64_t val;
 
+    if ( !v->domain->arch.hvm_domain.params[HVM_PARAM_HPET_ENABLED] )
+    {
+        result = ~0ul;
+        goto out;
+    }
+
     addr &= HPET_MMAP_SIZE-1;
 
     if ( hpet_check_access_length(addr, length) != 0 )
@@ -309,6 +315,9 @@ static int hpet_write(
 #define set_start_timer(n)   (__set_bit((n), &start_timers))
 #define set_restart_timer(n) (set_stop_timer(n),set_start_timer(n))
 
+    if ( !v->domain->arch.hvm_domain.params[HVM_PARAM_HPET_ENABLED] )
+        goto out;
+
     addr &= HPET_MMAP_SIZE-1;
 
     if ( hpet_check_access_length(addr, length) != 0 )
@@ -491,9 +500,8 @@ static int hpet_write(
 
 static int hpet_range(struct vcpu *v, unsigned long addr)
 {
-    return (v->domain->arch.hvm_domain.params[HVM_PARAM_HPET_ENABLED] &&
-            (addr >= HPET_BASE_ADDRESS) &&
-            (addr < (HPET_BASE_ADDRESS + HPET_MMAP_SIZE)));
+    return ( (addr >= HPET_BASE_ADDRESS) &&
+             (addr < (HPET_BASE_ADDRESS + HPET_MMAP_SIZE)) );
 }
 
 const struct hvm_mmio_handler hpet_mmio_handler = {
-- 
1.7.10.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel