Re: [Xen-devel] [PATCH V9 2/5] x86/hvm: pkeys, add pkeys support for guest_walk_tables

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Huaitong Han
> Sent: Wednesday, February 03, 2016 10:12 PM
> 
> Protection keys define a new 4-bit protection key field(PKEY) in bits 62:59 of
> leaf entries of the page tables.
> 
> PKRU register defines 32 bits, there are 16 domains and 2 attribute bits per
> domain in pkru, for each i (0 â i â 15), PKRU[2i] is the access-disable bit 
> for
> protection key i (ADi); PKRU[2i+1] is the write-disable bit for protection key
> i (WDi). PKEY is index to a defined domain.
> 
> A fault is considered as a PKU violation if all of the following conditions 
> are
> true:
> 1.CR4_PKE=1.
> 2.EFER_LMA=1.
> 3.Page is present with no reserved bit violations.
> 4.The access is not an instruction fetch.
> 5.The access is to a user page.
> 6.PKRU.AD=1
>     or The access is a data write and PKRU.WD=1
>                 and either CR0.WP=1 or it is a user access.
> 
> Signed-off-by: Huaitong Han <huaitong.han@xxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with one minor comment:

> --- a/xen/arch/x86/mm/guest_walk.c
> +++ b/xen/arch/x86/mm/guest_walk.c
> @@ -90,6 +90,54 @@ static uint32_t set_ad_bits(void *guest_p, void *walk_p, 
> int
> set_dirty)
>      return 0;
>  }
> 
> +#if GUEST_PAGING_LEVELS >= 4
> +static bool_t pkey_fault(struct vcpu *vcpu, uint32_t pfec,
> +        uint32_t pte_flags, uint32_t pte_pkey)
> +{
> +    uint32_t pkru = 0;
> +    bool_t pkru_ad = 0, pkru_wd = 0;
> +
> +    /* When page isn't present,  PKEY isn't checked. */
> +    if ( !(pfec & PFEC_page_present) || is_pv_vcpu(vcpu) )
> +        return 0;
> +
> +    /*
> +     * PKU:  additional mechanism by which the paging controls
> +     * access to user-mode addresses based on the value in the
> +     * PKRU register. A fault is considered as a PKU violation if all
> +     * of the following conditions are true:
> +     * 1.CR4_PKE=1.
> +     * 2.EFER_LMA=1.
> +     * 3.Page is present with no reserved bit violations.
> +     * 4.The access is not an instruction fetch.
> +     * 5.The access is to a user page.
> +     * 6.PKRU.AD=1 or
> +     *      the access is a data write and PKRU.WD=1 and
> +     *          either CR0.WP=1 or it is a user access.
> +     */
> +    if ( !hvm_pku_enabled(vcpu) ||
> +         !hvm_long_mode_enabled(vcpu) ||
> +         /* The persent bit is guaranteed by the caller. */

actually you do check present bit right before this trunk. Would
it be clearer to move earlier check here so to align with the
comment?

> +         (pfec & PFEC_reserved_bit) ||
> +         (pfec & PFEC_insn_fetch) ||
> +         !(pte_flags & _PAGE_USER) )
> +        return 0;
> +
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