Re: [Xen-devel] [PATCH V4 4/6] x86/hvm: pkeys, add pkeys support for guest_walk_tables

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.12.15 at 08:21, <huaitong.han@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/mm/guest_walk.c
> +++ b/xen/arch/x86/mm/guest_walk.c
> @@ -90,6 +90,55 @@ static uint32_t set_ad_bits(void *guest_p, void *walk_p, 
> int set_dirty)
>      return 0;
>  }
>  
> +#if GUEST_PAGING_LEVELS >= CONFIG_PAGING_LEVELS

GUEST_PAGING_LEVELS >= 4 (just like further down)

> +bool_t leaf_pte_pkeys_check(struct vcpu *vcpu,
> +        uint32_t pfec, uint32_t pte_pkey)
> +{
> +    unsigned int pkru = 0;
> +    bool_t pkru_ad, pkru_wd;
> +

Stray blank line.

> +    bool_t pf = !!(pfec & PFEC_page_present);
> +    bool_t uf = !!(pfec & PFEC_user_mode);
> +    bool_t wf = !!(pfec & PFEC_write_access);
> +    bool_t ff = !!(pfec & PFEC_insn_fetch);
> +    bool_t rsvdf = !!(pfec & PFEC_reserved_bit);
> +
> +    /* When page is present,  PFEC_prot_key is always checked */
> +    if ( !pf || is_pv_vcpu(vcpu) )
> +        return 0;

I think for a function called "check" together with how its callers use
it the return value meaning is inverted here. Also the comment seems
inverted wrt the actual check (and is missing a full stop). And doesn't
key 0 have static meaning, in which case you could bail early (and
namely avoid the expensive RDPKRU further down)?

> +    /*
> +     * 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 ture:
> +     * 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) || rsvdf || ff )

Where's the "user page" check? Also - indentation.

> +        return 0;
> +
> +    pkru = read_pkru();
> +    if ( unlikely(pkru) )
> +    {
> +        pkru_ad = read_pkru_ad(pkru, pte_pkey);
> +        pkru_wd = read_pkru_wd(pkru, pte_pkey);
> +        /* Condition 6 */
> +        if ( pkru_ad || (pkru_wd && wf && (hvm_wp_enabled(vcpu) || uf)))

Ah, uf is being checked here. But according to the comment it could
(and should, again to avoid the RDPKRU) move up.

> @@ -270,6 +324,12 @@ guest_walk_tables(struct vcpu *v, struct p2m_domain *p2m,
>  
>      pse2M = (gflags & _PAGE_PSE) && guest_supports_superpages(v); 
>  
> +#if GUEST_PAGING_LEVELS >= 4
> +    pkey = guest_l2e_get_pkey(gw->l2e);
> +    if ( pse2M && leaf_pte_pkeys_check(v, pfec, pkey) )
> +        rc |= _PAGE_PKEY_BITS;
> +#endif

I think the #ifdef isn't really needed here, if you moved the one
around leaf_pte_pkeys_check() into that function, and if you
perhaps also dropped the "pkey" local variable.

Jan


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