Re: [PATCH v12 47/60] i386/xen: handle PV timer hypercalls

[David Woodhouse <dwmw2@infradead.org>]

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On Mon, 2023-02-20 at 20:47 +0000, David Woodhouse wrote:
> @@ -1246,6 +1470,16 @@ static bool do_kvm_xen_handle_exit(X86CPU *cpu, struct kvm_xen_exit *exit)
>      }
>  
>      switch (code) {
> +    case __HYPERVISOR_set_timer_op:
> +        if (exit->u.hcall.longmode) {
> +            return kvm_xen_hcall_set_timer_op(exit, cpu,
> +                                              exit->u.hcall.params[0]);
> +        } else {
> +            /* In 32-bit mode, the 64-bit timer value is in two args. */
> +            uint64_t val = ((uint64_t)exit->u.hcall.params[1]) << 32 |
> +                (uint32_t)exit->u.hcall.params[0];
> +            return kvm_xen_hcall_set_timer_op(exit, cpu, val);
> +        }

Argh, there I'm returning -errno from a function that ought to set it
in exit->u.hcall.result and return 'true' for a handled syscall. Again.

Still *slightly* regretting my life choices there and wishing the
compiler caught that for me, but not enough to change it because we
really *do* want to track which unhandled calls guests are trying to
make. I'll fix it and then (if I make load_multiboot() tolerate 64-bit
binaries as previously discussed) the XTF tests work:

 $ ./bkvm/qemu-system-x86_64 -serial mon:stdio  -accel kvm,xen-version=0x4000a,kernel-irqchip=split -cpu host -display none -kernel$XTFDIR/tests/set_timer_op/test-hvm64-set_timer_op  
--- Xen Test Framework ---
Environment: HVM 64bit (Long mode 4 levels)
Test hypercall set_timer_op
Test result: SUCCESS
******************************
PANIC: xtf_exit(): hypercall_shutdown(SHUTDOWN_poweroff) returned
******************************
QEMU: Terminated
$ ./bkvm/qemu-system-x86_64 -serial mon:stdio  -accel kvm,xen-version=0x4000a,kernel-irqchip=split -cpu host -display none -kernel $XTFDIR/tests/set_timer_op/test-hvm32-set_timer_op  
--- Xen Test Framework ---
Environment: HVM 32bit (No paging)
Test hypercall set_timer_op
Test result: SUCCESS
******************************
PANIC: xtf_exit(): hypercall_shutdown(SHUTDOWN_poweroff) returned
******************************
QEMU: Terminated


(Dunno why it whines about poweroff; it isn't even calling the
hypercall. And the test to explicitly test that hypercall does work.)


--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -1118,14 +1118,18 @@ static int vcpuop_stop_singleshot_timer(CPUState *cs)
     return 0;
 }
 
-static int kvm_xen_hcall_set_timer_op(struct kvm_xen_exit *exit, X86CPU *cpu,
-                                      uint64_t timeout)
+static bool kvm_xen_hcall_set_timer_op(struct kvm_xen_exit *exit, X86CPU *cpu,
+                                       uint64_t timeout)
 {
+    int err;
+
     if (unlikely(timeout == 0)) {
-        return vcpuop_stop_singleshot_timer(CPU(cpu));
+        err = vcpuop_stop_singleshot_timer(CPU(cpu));
     } else {
-        return do_set_singleshot_timer(CPU(cpu), timeout, false, true);
+        err = do_set_singleshot_timer(CPU(cpu), timeout, false, true);
     }
+    exit->u.hcall.result = err;
+    return true;
 }
 
 static bool kvm_xen_hcall_vcpu_op(struct kvm_xen_exit *exit, X86CPU *cpu,


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