[Qemu-devel] [PATCH 28/31] vga: disable chain4_alias if KVM supports SMRAM

[Paolo Bonzini]

KVM is okay with SMRAM overlapping an MMIO area underneath it, but it does
not want to have two overlapping RAM slots for SMRAM and video RAM.
Unfortunately, the chain4_alias optimization results in the latter
situation.  Disable it if KVM supports system management mode.

Note that the chain4_alias optimization is misguided, because it assumes
that chain4 data is at VRAM address 0,1,2,3,4,5,6,7...16383.  This is
incorrect, because chain4 data is at VRAM address 0,1,2,3, 16,17,18,19,
..., 65523.  But we cannot fix the VRAM format without breaking migration,
so keep the optimization and just disable it if it gets in the way.

Signed-off-by: Paolo Bonzini <address@hidden>
---
 hw/display/vga.c     | 8 ++++++--
 hw/display/vga_int.h | 1 +
 include/sysemu/kvm.h | 1 +
 kvm-all.c            | 5 +++++
 kvm-stub.c           | 5 +++++
 5 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/hw/display/vga.c b/hw/display/vga.c
index d1d296c..b1925a0 100644
--- a/hw/display/vga.c
+++ b/hw/display/vga.c
@@ -154,7 +154,8 @@ static void vga_update_memory_access(VGACommonState *s)
         s->has_chain4_alias = false;
         s->plane_updated = 0xf;
     }
-    if ((s->sr[VGA_SEQ_PLANE_WRITE] & VGA_SR02_ALL_PLANES) ==
+    if (s->use_chain4_alias &&
+       (s->sr[VGA_SEQ_PLANE_WRITE] & VGA_SR02_ALL_PLANES) ==
         VGA_SR02_ALL_PLANES && s->sr[VGA_SEQ_MEMORY_MODE] & VGA_SR04_CHN_4M) {
         offset = 0;
         switch ((s->gr[VGA_GFX_MISC] >> 2) & 3) {
@@ -2219,8 +2220,11 @@ void vga_init(VGACommonState *s, Object *obj, 
MemoryRegion *address_space,
 
     qemu_register_reset(vga_reset, s);
 
-    s->bank_offset = 0;
+    if (!kvm_enabled() || !kvm_has_smm()) {
+        s->use_chain4_alias = true;
+    }
 
+    s->bank_offset = 0;
     s->legacy_address_space = address_space;
 
     vga_io_memory = vga_init_io(s, obj, &vga_ports, &vbe_ports);
diff --git a/hw/display/vga_int.h b/hw/display/vga_int.h
index fcfcc5f..646e64c 100644
--- a/hw/display/vga_int.h
+++ b/hw/display/vga_int.h
@@ -95,6 +95,7 @@ typedef struct VGACommonState {
     uint32_t vram_size_mb; /* property */
     uint32_t vbe_size;
     uint32_t latch;
+    bool use_chain4_alias;
     bool has_chain4_alias;
     MemoryRegion chain4_alias;
     uint8_t sr_index;
diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
index 4878959..e1db979 100644
--- a/include/sysemu/kvm.h
+++ b/include/sysemu/kvm.h
@@ -186,6 +186,7 @@ int kvm_has_pit_state2(void);
 int kvm_has_many_ioeventfds(void);
 int kvm_has_gsi_routing(void);
 int kvm_has_intx_set_mask(void);
+int kvm_has_smm(void);
 
 int kvm_init_vcpu(CPUState *cpu);
 int kvm_cpu_exec(CPUState *cpu);
diff --git a/kvm-all.c b/kvm-all.c
index 17a3771..5ad4877 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1990,6 +1990,11 @@ int kvm_vm_check_attr(KVMState *s, uint32_t group, 
uint64_t attr)
     return ret ? 0 : 1;
 }
 
+int kvm_has_smm(void)
+{
+    return kvm_check_extension(kvm_state, KVM_CAP_X86_SMM);
+}
+
 int kvm_has_sync_mmu(void)
 {
     return kvm_check_extension(kvm_state, KVM_CAP_SYNC_MMU);
diff --git a/kvm-stub.c b/kvm-stub.c
index 7ba90c5..c3428a5 100644
--- a/kvm-stub.c
+++ b/kvm-stub.c
@@ -56,6 +56,11 @@ int kvm_cpu_exec(CPUState *cpu)
     abort();
 }
 
+int kvm_has_smm(void)
+{
+    return 0;
+}
+
 int kvm_has_sync_mmu(void)
 {
     return 0;
-- 
1.8.3.1