Re: [PATCH 3/3] KVM: x86 emulator: Allow PM/VM86 switch during task switch

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jan 23, 2012 at 05:10:48PM +0100, Kevin Wolf wrote:
> Task switches can switch between Protected Mode and VM86. The current
> mode must be updated during the task switch emulation so that the new
> segment selectors are interpreted correctly and privilege checks
> succeed.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  arch/x86/include/asm/kvm_emulate.h |    1 +
>  arch/x86/kvm/emulate.c             |   17 +++++++++++++++++
>  arch/x86/kvm/x86.c                 |    6 ++++++
>  3 files changed, 24 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index c8a9cf3..4a21c7d 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -176,6 +176,7 @@ struct x86_emulate_ops {
>  	void (*set_idt)(struct x86_emulate_ctxt *ctxt, struct desc_ptr *dt);
>  	ulong (*get_cr)(struct x86_emulate_ctxt *ctxt, int cr);
>  	int (*set_cr)(struct x86_emulate_ctxt *ctxt, int cr, ulong val);
> +	void (*set_rflags)(struct x86_emulate_ctxt *ctxt, ulong val);
>  	int (*cpl)(struct x86_emulate_ctxt *ctxt);
>  	int (*get_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong *dest);
>  	int (*set_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong value);
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 833969e..52fce89 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2273,6 +2273,23 @@ static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,
>  		return emulate_gp(ctxt, 0);
>  	ctxt->_eip = tss->eip;
>  	ctxt->eflags = tss->eflags | 2;
> +
> +	/*
> +	 * If we're switching between Protected Mode and VM86, we need to make
> +	 * sure to update the mode before loading the segment descriptors so
> +	 * that the selectors are interpreted correctly.
> +	 *
> +	 * Need to get it to the vcpu struct immediately because it influences
> +	 * the CPL which is checked when loading the segment descriptors.
This is true only for VMX. SVM does not look at rflags. May be instead
of adding new x86_emulate_ops callback we need to get rid of get_cpl()
one and implement CPL checking using emulate.c:get_segment_selector().

> +	 */
> +	if (ctxt->eflags & X86_EFLAGS_VM)
> +		ctxt->mode = X86EMUL_MODE_VM86;
> +	else
> +		ctxt->mode = X86EMUL_MODE_PROT32;
> +
> +	ctxt->ops->set_rflags(ctxt, ctxt->eflags);
> +
> +	/* General purpose registers */
>  	ctxt->regs[VCPU_REGS_RAX] = tss->eax;
>  	ctxt->regs[VCPU_REGS_RCX] = tss->ecx;
>  	ctxt->regs[VCPU_REGS_RDX] = tss->edx;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index dc3e945..502b5c3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4040,6 +4040,11 @@ static int emulator_set_cr(struct x86_emulate_ctxt *ctxt, int cr, ulong val)
>  	return res;
>  }
>  
> +static void emulator_set_rflags(struct x86_emulate_ctxt *ctxt, ulong val)
> +{
> +	kvm_set_rflags(emul_to_vcpu(ctxt), val);
> +}
> +
>  static int emulator_get_cpl(struct x86_emulate_ctxt *ctxt)
>  {
>  	return kvm_x86_ops->get_cpl(emul_to_vcpu(ctxt));
> @@ -4199,6 +4204,7 @@ static struct x86_emulate_ops emulate_ops = {
>  	.set_idt	     = emulator_set_idt,
>  	.get_cr              = emulator_get_cr,
>  	.set_cr              = emulator_set_cr,
> +	.set_rflags          = emulator_set_rflags,
>  	.cpl                 = emulator_get_cpl,
>  	.get_dr              = emulator_get_dr,
>  	.set_dr              = emulator_set_dr,
> -- 
> 1.7.6.5

--
			Gleb.