Re: [PATCH] x86/shadow: Delete the none.c dummy file

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.02.2026 11:41, Alejandro Vallejo wrote:
> It only has 2 callers, both of which can be conditionally removed.
> 
> Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>
> ---
> I'd be ok conditionalising the else branch on...
> 
>     IS_ENABLED(CONFIG_SHADOW_PAGING )|| IS_ENABLED(CONFIG_LOG_DIRTY)
> 
> logdirty patch: 
> https://lore.kernel.org/xen-devel/20260209103118.5885-1-alejandro.garciavallejo@xxxxxxx
> 
> ... to avoid the danger of stale pointers, with required changes elsewhere so
> none.c is only compiled out in that case.

I'm not sure I understand this remark. Is this about something in the other
patch (which I haven't looked at yet), or ...

> --- a/xen/arch/x86/mm/paging.c
> +++ b/xen/arch/x86/mm/paging.c
> @@ -634,7 +634,7 @@ int paging_domain_init(struct domain *d)
>       */
>      if ( hap_enabled(d) )
>          hap_domain_init(d);
> -    else
> +    else if ( IS_ENABLED(CONFIG_SHADOW_PAGING) )
>          rc = shadow_domain_init(d);
>  
>      return rc;
> @@ -645,7 +645,7 @@ void paging_vcpu_init(struct vcpu *v)
>  {
>      if ( hap_enabled(v->domain) )
>          hap_vcpu_init(v);
> -    else
> +    else if ( IS_ENABLED(CONFIG_SHADOW_PAGING) )
>          shadow_vcpu_init(v);
>  }

... these two hunks? In this latter case, I don't think the bigger conditional
would be correct.

> --- a/xen/arch/x86/mm/shadow/none.c
> +++ /dev/null
> @@ -1,77 +0,0 @@
> -#include <xen/mm.h>
> -#include <asm/shadow.h>
> -
> -static int cf_check _toggle_log_dirty(struct domain *d)
> -{
> -    ASSERT(is_pv_domain(d));
> -    return -EOPNOTSUPP;
> -}
> -
> -static void cf_check _clean_dirty_bitmap(struct domain *d)
> -{
> -    ASSERT(is_pv_domain(d));
> -}
> -
> -static void cf_check _update_paging_modes(struct vcpu *v)
> -{
> -    ASSERT_UNREACHABLE();
> -}
> -
> -int shadow_domain_init(struct domain *d)
> -{
> -    /* For HVM set up pointers for safety, then fail. */
> -    static const struct log_dirty_ops sh_none_ops = {
> -        .enable  = _toggle_log_dirty,
> -        .disable = _toggle_log_dirty,
> -        .clean   = _clean_dirty_bitmap,
> -    };
> -
> -    paging_log_dirty_init(d, &sh_none_ops);

How do you avoid d->arch.paging.log_dirty.ops remaining NULL with this
removed?

> -    d->arch.paging.update_paging_modes = _update_paging_modes;

Same question for this function pointer.

> -    return is_hvm_domain(d) ? -EOPNOTSUPP : 0;
> -}
> -
> -static int cf_check _page_fault(
> -    struct vcpu *v, unsigned long va, struct cpu_user_regs *regs)
> -{
> -    ASSERT_UNREACHABLE();
> -    return 0;
> -}
> -
> -static bool cf_check _invlpg(struct vcpu *v, unsigned long linear)
> -{
> -    ASSERT_UNREACHABLE();
> -    return true;
> -}
> -
> -#ifdef CONFIG_HVM
> -static unsigned long cf_check _gva_to_gfn(
> -    struct vcpu *v, struct p2m_domain *p2m, unsigned long va, uint32_t *pfec)
> -{
> -    ASSERT_UNREACHABLE();
> -    return gfn_x(INVALID_GFN);
> -}
> -#endif
> -
> -static pagetable_t cf_check _update_cr3(struct vcpu *v, bool noflush)
> -{
> -    ASSERT_UNREACHABLE();
> -    return pagetable_null();
> -}
> -
> -static const struct paging_mode sh_paging_none = {
> -    .page_fault                    = _page_fault,
> -    .invlpg                        = _invlpg,
> -#ifdef CONFIG_HVM
> -    .gva_to_gfn                    = _gva_to_gfn,
> -#endif
> -    .update_cr3                    = _update_cr3,
> -};
> -
> -void shadow_vcpu_init(struct vcpu *v)
> -{
> -    ASSERT(is_pv_vcpu(v));
> -    v->arch.paging.mode = &sh_paging_none;

And the same question yet again for this pointer.

Jan