Re: [PATCH] kvm: x86: fix load xsave feature warning

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/07/2015 09:44, Wanpeng Li wrote:
> [   68.196974] WARNING: CPU: 1 PID: 2140 at arch/x86/kvm/x86.c:3161 kvm_arch_vcpu_ioctl+0xe88/0x1340 [kvm]()
> [   68.196975] Modules linked in: snd_hda_codec_hdmi i915 rfcomm bnep bluetooth i2c_algo_bit rfkill nfsd drm_kms_helper nfs_acl nfs drm lockd grace sunrpc fscache snd_hda_codec_realtek snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_seq_dummy snd_seq_oss x86_pkg_temp_thermal snd_seq_midi kvm_intel snd_seq_midi_event snd_rawmidi kvm snd_seq ghash_clmulni_intel fuse snd_timer aesni_intel parport_pc ablk_helper snd_seq_device cryptd ppdev snd lp parport lrw dcdbas gf128mul i2c_core glue_helper lpc_ich video shpchp mfd_core soundcore serio_raw acpi_cpufreq ext4 mbcache jbd2 sd_mod crc32c_intel ahci libahci libata e1000e ptp pps_core
> [   68.197005] CPU: 1 PID: 2140 Comm: qemu-system-x86 Not tainted 4.2.0-rc1+ #2
> [   68.197006] Hardware name: Dell Inc. OptiPlex 7020/0F5C5X, BIOS A03 01/08/2015
> [   68.197007]  ffffffffa03b0657 ffff8800d984bca8 ffffffff815915a2 0000000000000000
> [   68.197009]  0000000000000000 ffff8800d984bce8 ffffffff81057c0a 00007ff6d0001000
> [   68.197010]  0000000000000002 ffff880211c1a000 0000000000000004 ffff8800ce0288c0
> [   68.197012] Call Trace:
> [   68.197017]  [<ffffffff815915a2>] dump_stack+0x45/0x57
> [   68.197020]  [<ffffffff81057c0a>] warn_slowpath_common+0x8a/0xc0
> [   68.197022]  [<ffffffff81057cfa>] warn_slowpath_null+0x1a/0x20
> [   68.197029]  [<ffffffffa037bed8>] kvm_arch_vcpu_ioctl+0xe88/0x1340 [kvm]
> [   68.197035]  [<ffffffffa037aede>] ? kvm_arch_vcpu_load+0x4e/0x1c0 [kvm]
> [   68.197040]  [<ffffffffa03696a6>] kvm_vcpu_ioctl+0xc6/0x5c0 [kvm]
> [   68.197043]  [<ffffffff811252d2>] ? perf_pmu_enable+0x22/0x30
> [   68.197044]  [<ffffffff8112663e>] ? perf_event_context_sched_in+0x7e/0xb0
> [   68.197048]  [<ffffffff811a6882>] do_vfs_ioctl+0x2c2/0x4a0
> [   68.197050]  [<ffffffff8107bf33>] ? finish_task_switch+0x173/0x220
> [   68.197053]  [<ffffffff8123307f>] ? selinux_file_ioctl+0x4f/0xd0
> [   68.197055]  [<ffffffff8122cac3>] ? security_file_ioctl+0x43/0x60
> [   68.197057]  [<ffffffff811a6ad9>] SyS_ioctl+0x79/0x90
> [   68.197060]  [<ffffffff81597e57>] entry_SYSCALL_64_fastpath+0x12/0x6a
> [   68.197061] ---[ end trace 558a5ebf9445fc80 ]---
> 
> After commit (0c4109bec0 'x86/fpu/xstate: Fix up bad get_xsave_addr() 
> assumptions'), there is no assumption an xsave bit is present in the 
> hardware (pcntxt_mask) that it is always present in a given xsave buffer.
> An enabled state to be present on 'pcntxt_mask', but *not* in 'xstate_bv'
> could happen when the last 'xsave' did not request that this feature be 
> saved (unlikely) or because the "init optimization" caused it to not be 
> saved. This patch kill the assumption.
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> Note: This patch against latest linus tree.
> 
>  arch/x86/kvm/x86.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bbaf44e..7125cefe 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3157,8 +3157,7 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
>  			cpuid_count(XSTATE_CPUID, index,
>  				    &size, &offset, &ecx, &edx);
>  			memcpy(dest, src + offset, size);
> -		} else
> -			WARN_ON_ONCE(1);
> +		}
>  
>  		valid -= feature;
>  	}
> 

I'll apply this tomorrow, thanks.

Paolo