On 03/07/2015 15:49, Radim Krčmář wrote:
> fpu_activate is called outside of vcpu_load(), which means it should not
> touch VMCS, but fpu_activate needs to. Avoid the call by moving it to a
> point where we know that the guest needs eager FPU and VMCS is loaded.
>
> This will get rid of the following trace
>
> vmwrite error: reg 6800 value 0 (err 1)
> [<ffffffff8162035b>] dump_stack+0x19/0x1b
> [<ffffffffa046c701>] vmwrite_error+0x2c/0x2e [kvm_intel]
> [<ffffffffa045f26f>] vmcs_writel+0x1f/0x30 [kvm_intel]
> [<ffffffffa04617e5>] vmx_fpu_activate.part.61+0x45/0xb0 [kvm_intel]
> [<ffffffffa0461865>] vmx_fpu_activate+0x15/0x20 [kvm_intel]
> [<ffffffffa0560b91>] kvm_arch_vcpu_create+0x51/0x70 [kvm]
> [<ffffffffa0548011>] kvm_vm_ioctl+0x1c1/0x760 [kvm]
> [<ffffffff8118b55a>] ? handle_mm_fault+0x49a/0xec0
> [<ffffffff811e47d5>] do_vfs_ioctl+0x2e5/0x4c0
> [<ffffffff8127abbe>] ? file_has_perm+0xae/0xc0
> [<ffffffff811e4a51>] SyS_ioctl+0xa1/0xc0
> [<ffffffff81630949>] system_call_fastpath+0x16/0x1b
>
> (Note: we also unconditionally activate FPU in vmx_vcpu_reset(), so the
> removed code added nothing.)
>
> Fixes: c447e76b4cab ("kvm/fpu: Enable eager restore kvm FPU for MPX")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Vlastimil Holer <vlastimil.holer@xxxxxxxxx>
> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Andrey reported offlist that the bug went away by reverting 1cde293. So
the patch would at least need a new commit message. :)
I'm putting it on hold.
Paolo
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