Re: [PATCH] Revert "kvm: x86: Use task structs fpu field for user"

On Mon, 22 Jul 2019 at 20:49, Paolo Bonzini pbonzini@redhat.com wrote:

This reverts commit 240c35a3783ab9b3a0afaba0dde7291295680a6b ("kvm: x86: Use task structs fpu field for user", 2018-11-06). The commit is broken and causes QEMU's FPU state to be destroyed when KVM_RUN is preempted.

Fixes: 240c35a3783a ("kvm: x86: Use task structs fpu field for user") Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com

---

arch/x86/include/asm/kvm_host.h | 7 ++++--- arch/x86/kvm/x86.c | 4 ++-- 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 0cc5b611a113..b2f1ffb937af 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -607,15 +607,16 @@ struct kvm_vcpu_arch {

    /*
     * QEMU userspace and the guest each have their own FPU state.

•    * In vcpu_run, we switch between the user, maintained in the
  

•    * task_struct struct, and guest FPU contexts. While running a VCPU,
  

•    * the VCPU thread will have the guest FPU context.
  

•    * In vcpu_run, we switch between the user and guest FPU contexts.
  

•    * While running a VCPU, the VCPU thread will have the guest FPU
  

•    * context.
     *
     * Note that while the PKRU state lives inside the fpu registers,
     * it is switched out separately at VMENTER and VMEXIT time. The
     * "guest_fpu" state here contains the guest FPU context, with the
     * host PRKU bits.
     */
  

•   struct fpu user_fpu;
    struct fpu *guest_fpu;
  
    u64 xcr0;
  

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 58305cf81182..cf2afdf8facf 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8270,7 +8270,7 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu) { fpregs_lock();

•   copy_fpregs_to_fpstate(&current->thread.fpu);
  

•   copy_fpregs_to_fpstate(&vcpu->arch.user_fpu);
    /* PKRU is separately restored in kvm_x86_ops->run.  */
    __copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,
                            ~XFEATURE_MASK_PKRU);
  

@@ -8287,7 +8287,7 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu) fpregs_lock();

    copy_fpregs_to_fpstate(vcpu->arch.guest_fpu);

•   copy_kernel_to_fpregs(&current->thread.fpu.state);
  

•   copy_kernel_to_fpregs(&vcpu->arch.user_fpu.state);
  
    fpregs_mark_activate();
    fpregs_unlock();
  

Looks good to me.

Regards, Wanpeng Li