linux-kernel - Re: [PATCH 2/2] KVM: X86: Add a capability to configure bus frequency for APIC timer

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Message-ID: <ZU5BSSg_AbJnec7j@google.com>
Date:   Fri, 10 Nov 2023 06:42:17 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     kernel test robot <yujie.liu@...el.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, oe-kbuild-all@...ts.linux.dev,
        isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        erdemaktas@...gle.com, Vishal Annapurve <vannapurve@...gle.com>
Subject: Re: [PATCH 2/2] KVM: X86: Add a capability to configure bus frequency
 for APIC timer

On Fri, Nov 10, 2023, kernel test robot wrote:
> Hi,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on kvm/queue]
> [also build test ERROR on linus/master next-20231109]
> [cannot apply to mst-vhost/linux-next kvm/linux-next v6.6]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/isaku-yamahata-intel-com/KVM-x86-Make-the-hardcoded-APIC-bus-frequency-vm-variable/20231108-032736
> base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git queue
> patch link:    https://lore.kernel.org/r/70c2a2277f57b804c715c5b4b4aa0b3561ed6a4f.1699383993.git.isaku.yamahata%40intel.com
> patch subject: [PATCH 2/2] KVM: X86: Add a capability to configure bus frequency for APIC timer
> config: i386-buildonly-randconfig-002-20231109 (https://download.01.org/0day-ci/archive/20231110/202311100209.zIaZqZhg-lkp@intel.com/config)
> compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231110/202311100209.zIaZqZhg-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <yujie.liu@...el.com>
> | Closes: https://lore.kernel.org/r/202311100209.zIaZqZhg-lkp@intel.com/
> 
> All errors (this is a 32-bit build, new ones prefixed by >>):
> 
>    ld: arch/x86/kvm/x86.o: in function `kvm_vm_ioctl_enable_cap':
> >> x86.c:(.text+0x1265b): undefined reference to `__udivdi3'

Heh, this inscrutable error is due to 64-bit division on 32-bit kernels.

	u64 bus_frequency = cap->args[0];
	u64 bus_cycle_ns;

	if (!bus_frequency)
		return -EINVAL;

	bus_cycle_ns = 1000000000UL / bus_frequency;  <========

I don't see any reason to allow 64-bit values, e.g. Intel's CPUID 0x15 only
supports a 32-bit frequency in Hz.  I.e. just truncate it to a u32.