Re: [Xen-devel] [PATCH V3] x86/hvm: fix domain crash when CR3 has the noflush bit set

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.02.18 at 09:14, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> @@ -2313,6 +2314,12 @@ int hvm_set_cr3(unsigned long value, bool_t may_defer)
>          }
>      }
>  
> +    if ( hvm_pcid_enabled(v) ) /* Clear the noflush bit. */
> +    {
> +        noflush = !!(value & X86_CR3_NOFLUSH);

Pointless !!.

> --- a/xen/include/asm-x86/hvm/hvm.h
> +++ b/xen/include/asm-x86/hvm/hvm.h
> @@ -34,6 +34,9 @@ extern bool_t opt_hvm_fep;
>  #define opt_hvm_fep 0
>  #endif
>  
> +#define X86_CR3_NOFLUSH (1ull << 63)

This belongs in x86-defs.h

> +#define X86_CR3_NOFLUSH_DISABLE_MASK (X86_CR3_NOFLUSH - 1)

This shouldn't be needed (use ~X86_CR3_NOFLUSH instead).

> @@ -322,9 +325,10 @@ hvm_update_host_cr3(struct vcpu *v)
>          hvm_funcs.update_host_cr3(v);
>  }
>  
> -static inline void hvm_update_guest_cr(struct vcpu *v, unsigned int cr)
> +static inline void hvm_update_guest_cr(struct vcpu *v, unsigned int cr,
> +                                       bool noflush)
>  {
> -    hvm_funcs.update_guest_cr(v, cr);
> +    hvm_funcs.update_guest_cr(v, cr, noflush);
>  }

Instead of altering this function (and a lot of callers), how about
introducing

static inline void hvm_update_guest_cr3(struct vcpu *v, bool noflush)
{
    hvm_funcs.update_guest_cr(v, 3, noflush);
}

? I'm also not convinced of the update_guest_cr() hook taking a
bool which is meaningless for all other CRs. Perhaps a more general
flags parameter would be better, with CR-specific meaning (you'd
then e.g. introduce HVM_UPDATE_GUEST_CR3_NO_FLUSH).

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel