[v6,06/11] hvf: Simplify post reset/init/loadvm hooks

Commit Message

Alexander Graf Jan. 20, 2021, 10:44 p.m. UTC

The hooks we have that call us after reset, init and loadvm really all
just want to say "The reference of all register state is in the QEMU
vcpu struct, please push it".

We already have a working pushing mechanism though called cpu->vcpu_dirty,
so we can just reuse that for all of the above, syncing state properly the
next time we actually execute a vCPU.

This fixes PSCI resets on ARM, as they modify CPU state even after the
post init call has completed, but before we execute the vCPU again.

To also make the scheme work for x86, we have to make sure we don't
move stale eflags into our env when the vcpu state is dirty.

Signed-off-by: Alexander Graf <[e-mail]>
Reviewed-by: Roman Bolshakov <[e-mail]>
Tested-by: Roman Bolshakov <[e-mail]>
---
 accel/hvf/hvf-cpus.c     | 27 +++++++--------------------
 target/i386/hvf/x86hvf.c |  5 ++++-
 2 files changed, 11 insertions(+), 21 deletions(-)

Comments

Peter Maydell Jan. 28, 2021, 3:28 p.m. UTC | #1

On Wed, 20 Jan 2021 at 22:44, Alexander Graf <[e-mail]> wrote:
>
> The hooks we have that call us after reset, init and loadvm really all
> just want to say "The reference of all register state is in the QEMU
> vcpu struct, please push it".
>
> We already have a working pushing mechanism though called cpu->vcpu_dirty,
> so we can just reuse that for all of the above, syncing state properly the
> next time we actually execute a vCPU.
>
> This fixes PSCI resets on ARM, as they modify CPU state even after the
> post init call has completed, but before we execute the vCPU again.
>
> To also make the scheme work for x86, we have to make sure we don't
> move stale eflags into our env when the vcpu state is dirty.
>
> Signed-off-by: Alexander Graf <[e-mail]>
> Reviewed-by: Roman Bolshakov <[e-mail]>
> Tested-by: Roman Bolshakov <[e-mail]>

What's the difference between HVF and KVM that means this code
doesn't have the same structure the KVM code does here?

thanks
-- PMM

Alexander Graf Feb. 10, 2021, 9:34 p.m. UTC | #2

On 28.01.21 16:28, Peter Maydell wrote:
> On Wed, 20 Jan 2021 at 22:44, Alexander Graf <[e-mail]> wrote:
>> The hooks we have that call us after reset, init and loadvm really all
>> just want to say "The reference of all register state is in the QEMU
>> vcpu struct, please push it".
>>
>> We already have a working pushing mechanism though called cpu->vcpu_dirty,
>> so we can just reuse that for all of the above, syncing state properly the
>> next time we actually execute a vCPU.
>>
>> This fixes PSCI resets on ARM, as they modify CPU state even after the
>> post init call has completed, but before we execute the vCPU again.
>>
>> To also make the scheme work for x86, we have to make sure we don't
>> move stale eflags into our env when the vcpu state is dirty.
>>
>> Signed-off-by: Alexander Graf <[e-mail]>
>> Reviewed-by: Roman Bolshakov <[e-mail]>
>> Tested-by: Roman Bolshakov <[e-mail]>
> What's the difference between HVF and KVM that means this code
> doesn't have the same structure the KVM code does here?


The main reason is that with KVM, responsibility of register reset is 
shared between kernel and user space. With HVF, user space has 
everything under full control, so all we need to say is "user space is 
your reference now". While with KVM, we may need to still say "KVM state 
is your reference, because it will do the register reset on behalf of us".

Alex

Patch

diff --git a/accel/hvf/hvf-cpus.c b/accel/hvf/hvf-cpus.c
index 2c6796604a..a324da2757 100644
--- a/accel/hvf/hvf-cpus.c
+++ b/accel/hvf/hvf-cpus.c
@@ -275,39 +275,26 @@  static void hvf_cpu_synchronize_state(CPUState *cpu)
     }
 }
 
-static void do_hvf_cpu_synchronize_post_reset(CPUState *cpu,
-                                              run_on_cpu_data arg)
+static void do_hvf_cpu_synchronize_set_dirty(CPUState *cpu,
+                                             run_on_cpu_data arg)
 {
-    hvf_put_registers(cpu);
-    cpu->vcpu_dirty = false;
+    /* QEMU state is the reference, push it to HVF now and on next entry */
+    cpu->vcpu_dirty = true;
 }
 
 static void hvf_cpu_synchronize_post_reset(CPUState *cpu)
 {
-    run_on_cpu(cpu, do_hvf_cpu_synchronize_post_reset, RUN_ON_CPU_NULL);
-}
-
-static void do_hvf_cpu_synchronize_post_init(CPUState *cpu,
-                                             run_on_cpu_data arg)
-{
-    hvf_put_registers(cpu);
-    cpu->vcpu_dirty = false;
+    run_on_cpu(cpu, do_hvf_cpu_synchronize_set_dirty, RUN_ON_CPU_NULL);
 }
 
 static void hvf_cpu_synchronize_post_init(CPUState *cpu)
 {
-    run_on_cpu(cpu, do_hvf_cpu_synchronize_post_init, RUN_ON_CPU_NULL);
-}
-
-static void do_hvf_cpu_synchronize_pre_loadvm(CPUState *cpu,
-                                              run_on_cpu_data arg)
-{
-    cpu->vcpu_dirty = true;
+    run_on_cpu(cpu, do_hvf_cpu_synchronize_set_dirty, RUN_ON_CPU_NULL);
 }
 
 static void hvf_cpu_synchronize_pre_loadvm(CPUState *cpu)
 {
-    run_on_cpu(cpu, do_hvf_cpu_synchronize_pre_loadvm, RUN_ON_CPU_NULL);
+    run_on_cpu(cpu, do_hvf_cpu_synchronize_set_dirty, RUN_ON_CPU_NULL);
 }
 
 static void hvf_vcpu_destroy(CPUState *cpu)
diff --git a/target/i386/hvf/x86hvf.c b/target/i386/hvf/x86hvf.c
index 0f2aeb1cf8..3111c0be4c 100644
--- a/target/i386/hvf/x86hvf.c
+++ b/target/i386/hvf/x86hvf.c
@@ -435,7 +435,10 @@  int hvf_process_events(CPUState *cpu_state)
     X86CPU *cpu = X86_CPU(cpu_state);
     CPUX86State *env = &cpu->env;
 
-    env->eflags = rreg(cpu_state->hvf->fd, HV_X86_RFLAGS);
+    if (!cpu_state->vcpu_dirty) {
+        /* light weight sync for CPU_INTERRUPT_HARD and IF_MASK */
+        env->eflags = rreg(cpu_state->hvf->fd, HV_X86_RFLAGS);
+    }
 
     if (cpu_state->interrupt_request & CPU_INTERRUPT_INIT) {
         cpu_synchronize_state(cpu_state);