Re: [Qemu-devel] centos 7.2 guest doesn't boot without kvmvapic in TCG mode

[Xu, Anthony]

+ Richard Henderson

Anthony

> -----Original Message-----
> From: Xu, Anthony
> Sent: Tuesday, April 4, 2017 5:19 PM
> To: 'address@hidden' <address@hidden>
> Cc: 'Paolo Bonzini' <address@hidden>; 'Stefan Hajnoczi'
> <address@hidden>
> Subject: [Qemu-devel] centos 7.2 guest doesn't boot without kvmvapic in
> TCG mode
> 
> I disabled kvmvapic by
> 
> diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
> index c3829e3..52be2b0 100644
> --- a/hw/intc/apic_common.c
> +++ b/hw/intc/apic_common.c
> @@ -440,7 +440,7 @@ static const VMStateDescription
> vmstate_apic_common = {
>  static Property apic_properties_common[] = {
>      DEFINE_PROP_UINT8("version", APICCommonState, version, 0x14),
>      DEFINE_PROP_BIT("vapic", APICCommonState, vapic_control,
> VAPIC_ENABLE_BIT,
> -                    true),
> +                    false),
>      DEFINE_PROP_BOOL("legacy-instance-id", APICCommonState,
> legacy_instance_id,
>                       false),
>      DEFINE_PROP_END_OF_LIST(),
> 
> 
> Tried to boot centos guest with this command
> 
> ./x86_64-softmmu/qemu-system-x86_64 -bios
> /home/root/guest/seabios.bin
> -machine q35 -m 1G -drive
> format=raw,file=/home/root/images/centos7.2.img,if=ide,index=0
> -nographic  -nodefaults  -serial pty -monitor pty
> -chardev stdio,id=seabios -device isa-
> debugcon,iobase=0x402,chardev=seabios
> 
> 
> Seabios complained
> 
> Seabios output
> "
> Booting from Hard Disk...
> WARNING - Timeout at ahci_command:154!
> Boot failed: could not read the boot disk
> 
> enter handle_18:
>   NULL
> Booting from Floppy...
> Boot failed: could not read the boot disk
> 
> enter handle_18:
>   NULL
> No bootable device.
> "
> 
> It can boot with kvmvapic enabled by using the same command.
> 
> Seabios output
> "
> Booting from Hard Disk...
> Booting from 0000:7c00
> "
> 
> In the original commit,
> " Therefore, the VAPI is enabled by default, even in TCG mode. Here, no
> speedup can be achieved as the emulation overhead of the TPR register is
> marginal compared to instruction emulation."
> 
> Seems no performance benefit for TCG mode
> What's the other benefit of using kvmvapic in TCG mode?
> 
> Should we make TCG mode work without kvmvapic?
> 
> If we don't need to use kvmvapic in TCG mode,
> we can make kvmvapic code clearer by removing all TCG related code in
> kvmvapic.c.
> 
> 
> Anthony