From: Denis Mukhin <dmkhn@proton.me>

From: Denis Mukhin <dmukhin@ford.com>

Add new flag to domain structure for marking permission to intercept
the physical console input by the domain.

Update console input switch logic accordingly.

No functional change intended.

Signed-off-by: Denis Mukhin <dmukhin@ford.com>
---
Changes since v3:
- rebased
---
 xen/arch/arm/vpl011.c      |  2 ++
 xen/arch/x86/pv/shim.c     |  2 ++
 xen/common/domain.c        |  2 ++
 xen/drivers/char/console.c | 18 +++++++++++++++++-
 xen/include/xen/sched.h    |  8 +++++++-
 5 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index 66047bf33c..147958eee8 100644
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -737,6 +737,8 @@ int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
     register_mmio_handler(d, &vpl011_mmio_handler,
                           vpl011->base_addr, GUEST_PL011_SIZE, NULL);
 
+    d->console.input_allowed = true;
+
     return 0;
 
 out1:
diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
index c506cc0bec..bc2a7dd5fa 100644
--- a/xen/arch/x86/pv/shim.c
+++ b/xen/arch/x86/pv/shim.c
@@ -238,6 +238,8 @@ void __init pv_shim_setup_dom(struct domain *d, l4_pgentry_t *l4start,
      * guest from depleting the shim memory pool.
      */
     d->max_pages = domain_tot_pages(d);
+
+    d->console.input_allowed = true;
 }
 
 static void write_start_info(struct domain *d)
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 87e5be35e5..9bc66d80c4 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -835,6 +835,8 @@ struct domain *domain_create(domid_t domid,
         flags |= CDF_hardware;
         if ( old_hwdom )
             old_hwdom->cdf &= ~CDF_hardware;
+
+        d->console.input_allowed = true;
     }
 
     /* Holding CDF_* internal flags. */
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 30701ae0b0..8a0bcff78f 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -512,9 +512,21 @@ static unsigned int __read_mostly console_rx = 0;
 
 struct domain *console_get_domain(void)
 {
+    struct domain *d;
+
     if ( console_rx == 0 )
             return NULL;
-    return rcu_lock_domain_by_id(console_rx - 1);
+
+    d = rcu_lock_domain_by_id(console_rx - 1);
+    if ( !d )
+        return NULL;
+
+    if ( d->console.input_allowed )
+        return d;
+
+    rcu_unlock_domain(d);
+
+    return NULL;
 }
 
 void console_put_domain(struct domain *d)
@@ -551,6 +563,10 @@ static void console_switch_input(void)
         if ( d )
         {
             rcu_unlock_domain(d);
+
+            if ( !d->console.input_allowed )
+                break;
+
             console_rx = next_rx;
             printk("*** Serial input to DOM%u", domid);
             break;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 559d201e0c..e91c99a8f3 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -512,7 +512,7 @@ struct domain
     bool             auto_node_affinity;
     /* Is this guest fully privileged (aka dom0)? */
     bool             is_privileged;
-    /* Can this guest access the Xen console? */
+    /* XSM: permission to use HYPERCALL_console_io hypercall */
     bool             is_console;
     /* Is this guest being debugged by dom0? */
     bool             debugger_attached;
@@ -651,6 +651,12 @@ struct domain
     unsigned int num_llc_colors;
     const unsigned int *llc_colors;
 #endif
+
+    /* Console settings. */
+    struct {
+        /* Permission to take ownership of the physical console input. */
+        bool input_allowed;
+    } console;
 } __aligned(PAGE_SIZE);
 
 static inline struct page_list_head *page_to_list(
-- 
2.34.1

On Thu, 29 May 2025, dmkhn@proton.me wrote:
> Add new flag to domain structure for marking permission to intercept
> the physical console input by the domain.
> 
> Update console input switch logic accordingly.
> 
> No functional change intended.
> 
> Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> ---
> Changes since v3:
> - rebased
> ---
>  xen/arch/arm/vpl011.c      |  2 ++
>  xen/arch/x86/pv/shim.c     |  2 ++
>  xen/common/domain.c        |  2 ++
>  xen/drivers/char/console.c | 18 +++++++++++++++++-
>  xen/include/xen/sched.h    |  8 +++++++-
>  5 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
> index 66047bf33c..147958eee8 100644
> --- a/xen/arch/arm/vpl011.c
> +++ b/xen/arch/arm/vpl011.c
> @@ -737,6 +737,8 @@ int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
>      register_mmio_handler(d, &vpl011_mmio_handler,
>                            vpl011->base_addr, GUEST_PL011_SIZE, NULL);
>  
> +    d->console.input_allowed = true;

This should be set only when backend_in_domain = false.


>      return 0;
>  
>  out1:
> diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
> index c506cc0bec..bc2a7dd5fa 100644
> --- a/xen/arch/x86/pv/shim.c
> +++ b/xen/arch/x86/pv/shim.c
> @@ -238,6 +238,8 @@ void __init pv_shim_setup_dom(struct domain *d, l4_pgentry_t *l4start,
>       * guest from depleting the shim memory pool.
>       */
>      d->max_pages = domain_tot_pages(d);
> +
> +    d->console.input_allowed = true;
>  }
>  
>  static void write_start_info(struct domain *d)
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index 87e5be35e5..9bc66d80c4 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -835,6 +835,8 @@ struct domain *domain_create(domid_t domid,
>          flags |= CDF_hardware;
>          if ( old_hwdom )
>              old_hwdom->cdf &= ~CDF_hardware;
> +
> +        d->console.input_allowed = true;
>      }
>  
>      /* Holding CDF_* internal flags. */
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 30701ae0b0..8a0bcff78f 100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -512,9 +512,21 @@ static unsigned int __read_mostly console_rx = 0;
>  
>  struct domain *console_get_domain(void)
>  {
> +    struct domain *d;
> +
>      if ( console_rx == 0 )
>              return NULL;
> -    return rcu_lock_domain_by_id(console_rx - 1);
> +
> +    d = rcu_lock_domain_by_id(console_rx - 1);
> +    if ( !d )
> +        return NULL;
> +
> +    if ( d->console.input_allowed )
> +        return d;
> +
> +    rcu_unlock_domain(d);
> +
> +    return NULL;

The original idea was to skip over domains that cannot have any input so
I don't think we should get in this situation. We could even have an
assert.


>  }
>  
>  void console_put_domain(struct domain *d)
> @@ -551,6 +563,10 @@ static void console_switch_input(void)
>          if ( d )
>          {
>              rcu_unlock_domain(d);
> +
> +            if ( !d->console.input_allowed )
> +                break;

shouldn't this be continue instead of break?


>              console_rx = next_rx;
>              printk("*** Serial input to DOM%u", domid);
>              break;
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 559d201e0c..e91c99a8f3 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -512,7 +512,7 @@ struct domain
>      bool             auto_node_affinity;
>      /* Is this guest fully privileged (aka dom0)? */
>      bool             is_privileged;
> -    /* Can this guest access the Xen console? */
> +    /* XSM: permission to use HYPERCALL_console_io hypercall */
>      bool             is_console;

While I am in favor of this direction and we certainly need a better way
to distinguish domains that can use HYPERCALL_console_io hypercall from
others, could we simplify this and just assume that "is_console" implies
input_allowed and also set is_console = true in all the same places you
are setting input_allowed = true in this patch?

For clarity, I am suggesting:
- do not add input_allowed
- set is_console = true in domain_vpl011_init, pv_shim_setup_dom, etc.

The only side effect is that we would allow domains with vpl011 to also
use console hypercalls but I don't think there is any harm in that?

I don't feel strongly about this, I am just trying to find ways to make
things simple. I apologize if it was already discussed during review of
one of the previous versions.

I am also OK with this approach.


>      /* Is this guest being debugged by dom0? */
>      bool             debugger_attached;
> @@ -651,6 +651,12 @@ struct domain
>      unsigned int num_llc_colors;
>      const unsigned int *llc_colors;
>  #endif
> +
> +    /* Console settings. */
> +    struct {
> +        /* Permission to take ownership of the physical console input. */
> +        bool input_allowed;
> +    } console;
>  } __aligned(PAGE_SIZE);
>  
>  static inline struct page_list_head *page_to_list(
> -- 
> 2.34.1
> 
>

On Thu, May 29, 2025 at 05:58:00PM -0700, Stefano Stabellini wrote:
> On Thu, 29 May 2025, dmkhn@proton.me wrote:
> > Add new flag to domain structure for marking permission to intercept
> > the physical console input by the domain.
> >
> > Update console input switch logic accordingly.
> >
> > No functional change intended.
> >
> > Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> > ---
> > Changes since v3:
> > - rebased
> > ---
> >  xen/arch/arm/vpl011.c      |  2 ++
> >  xen/arch/x86/pv/shim.c     |  2 ++
> >  xen/common/domain.c        |  2 ++
> >  xen/drivers/char/console.c | 18 +++++++++++++++++-
> >  xen/include/xen/sched.h    |  8 +++++++-
> >  5 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
> > index 66047bf33c..147958eee8 100644
> > --- a/xen/arch/arm/vpl011.c
> > +++ b/xen/arch/arm/vpl011.c
> > @@ -737,6 +737,8 @@ int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
> >      register_mmio_handler(d, &vpl011_mmio_handler,
> >                            vpl011->base_addr, GUEST_PL011_SIZE, NULL);
> >
> > +    d->console.input_allowed = true;
> 
> This should be set only when backend_in_domain = false.
> 
> 
> >      return 0;
> >
> >  out1:
> > diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
> > index c506cc0bec..bc2a7dd5fa 100644
> > --- a/xen/arch/x86/pv/shim.c
> > +++ b/xen/arch/x86/pv/shim.c
> > @@ -238,6 +238,8 @@ void __init pv_shim_setup_dom(struct domain *d, l4_pgentry_t *l4start,
> >       * guest from depleting the shim memory pool.
> >       */
> >      d->max_pages = domain_tot_pages(d);
> > +
> > +    d->console.input_allowed = true;
> >  }
> >
> >  static void write_start_info(struct domain *d)
> > diff --git a/xen/common/domain.c b/xen/common/domain.c
> > index 87e5be35e5..9bc66d80c4 100644
> > --- a/xen/common/domain.c
> > +++ b/xen/common/domain.c
> > @@ -835,6 +835,8 @@ struct domain *domain_create(domid_t domid,
> >          flags |= CDF_hardware;
> >          if ( old_hwdom )
> >              old_hwdom->cdf &= ~CDF_hardware;
> > +
> > +        d->console.input_allowed = true;
> >      }
> >
> >      /* Holding CDF_* internal flags. */
> > diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> > index 30701ae0b0..8a0bcff78f 100644
> > --- a/xen/drivers/char/console.c
> > +++ b/xen/drivers/char/console.c
> > @@ -512,9 +512,21 @@ static unsigned int __read_mostly console_rx = 0;
> >
> >  struct domain *console_get_domain(void)
> >  {
> > +    struct domain *d;
> > +
> >      if ( console_rx == 0 )
> >              return NULL;
> > -    return rcu_lock_domain_by_id(console_rx - 1);
> > +
> > +    d = rcu_lock_domain_by_id(console_rx - 1);
> > +    if ( !d )
> > +        return NULL;
> > +
> > +    if ( d->console.input_allowed )
> > +        return d;
> > +
> > +    rcu_unlock_domain(d);
> > +
> > +    return NULL;
> 
> The original idea was to skip over domains that cannot have any input so
> I don't think we should get in this situation. We could even have an
> assert.
> 
> 
> >  }
> >
> >  void console_put_domain(struct domain *d)
> > @@ -551,6 +563,10 @@ static void console_switch_input(void)
> >          if ( d )
> >          {
> >              rcu_unlock_domain(d);
> > +
> > +            if ( !d->console.input_allowed )
> > +                break;
> 
> shouldn't this be continue instead of break?
> 
> 
> >              console_rx = next_rx;
> >              printk("*** Serial input to DOM%u", domid);
> >              break;
> > diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> > index 559d201e0c..e91c99a8f3 100644
> > --- a/xen/include/xen/sched.h
> > +++ b/xen/include/xen/sched.h
> > @@ -512,7 +512,7 @@ struct domain
> >      bool             auto_node_affinity;
> >      /* Is this guest fully privileged (aka dom0)? */
> >      bool             is_privileged;
> > -    /* Can this guest access the Xen console? */
> > +    /* XSM: permission to use HYPERCALL_console_io hypercall */
> >      bool             is_console;
> 
> While I am in favor of this direction and we certainly need a better way
> to distinguish domains that can use HYPERCALL_console_io hypercall from
> others, could we simplify this and just assume that "is_console" implies
> input_allowed and also set is_console = true in all the same places you
> are setting input_allowed = true in this patch?
> 
> For clarity, I am suggesting:
> - do not add input_allowed
> - set is_console = true in domain_vpl011_init, pv_shim_setup_dom, etc.
> 
> The only side effect is that we would allow domains with vpl011 to also
> use console hypercalls but I don't think there is any harm in that?
> 
> I don't feel strongly about this, I am just trying to find ways to make
> things simple. I apologize if it was already discussed during review of
> one of the previous versions.

There was feedback on using is_console:

  https://lore.kernel.org/xen-devel/e899f63b-6182-4b53-9fb4-9a821e75648b@suse.com/

AFAIU, since XSM is the existing user of is_console, there should be a new
separate flag to avoid collision with the existing one.

> 
> I am also OK with this approach.
> 
> 
> >      /* Is this guest being debugged by dom0? */
> >      bool             debugger_attached;
> > @@ -651,6 +651,12 @@ struct domain
> >      unsigned int num_llc_colors;
> >      const unsigned int *llc_colors;
> >  #endif
> > +
> > +    /* Console settings. */
> > +    struct {
> > +        /* Permission to take ownership of the physical console input. */
> > +        bool input_allowed;
> > +    } console;
> >  } __aligned(PAGE_SIZE);
> >
> >  static inline struct page_list_head *page_to_list(
> > --
> > 2.34.1
> >
> >
> 

On Fri, 30 May 2025, dmkhn@proton.me wrote:
> On Thu, May 29, 2025 at 05:58:00PM -0700, Stefano Stabellini wrote:
> > On Thu, 29 May 2025, dmkhn@proton.me wrote:
> > > Add new flag to domain structure for marking permission to intercept
> > > the physical console input by the domain.
> > >
> > > Update console input switch logic accordingly.
> > >
> > > No functional change intended.
> > >
> > > Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> > > ---
> > > Changes since v3:
> > > - rebased
> > > ---
> > >  xen/arch/arm/vpl011.c      |  2 ++
> > >  xen/arch/x86/pv/shim.c     |  2 ++
> > >  xen/common/domain.c        |  2 ++
> > >  xen/drivers/char/console.c | 18 +++++++++++++++++-
> > >  xen/include/xen/sched.h    |  8 +++++++-
> > >  5 files changed, 30 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
> > > index 66047bf33c..147958eee8 100644
> > > --- a/xen/arch/arm/vpl011.c
> > > +++ b/xen/arch/arm/vpl011.c
> > > @@ -737,6 +737,8 @@ int domain_vpl011_init(struct domain *d, struct vpl011_init_info *info)
> > >      register_mmio_handler(d, &vpl011_mmio_handler,
> > >                            vpl011->base_addr, GUEST_PL011_SIZE, NULL);
> > >
> > > +    d->console.input_allowed = true;
> > 
> > This should be set only when backend_in_domain = false.
> > 
> > 
> > >      return 0;
> > >
> > >  out1:
> > > diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
> > > index c506cc0bec..bc2a7dd5fa 100644
> > > --- a/xen/arch/x86/pv/shim.c
> > > +++ b/xen/arch/x86/pv/shim.c
> > > @@ -238,6 +238,8 @@ void __init pv_shim_setup_dom(struct domain *d, l4_pgentry_t *l4start,
> > >       * guest from depleting the shim memory pool.
> > >       */
> > >      d->max_pages = domain_tot_pages(d);
> > > +
> > > +    d->console.input_allowed = true;
> > >  }
> > >
> > >  static void write_start_info(struct domain *d)
> > > diff --git a/xen/common/domain.c b/xen/common/domain.c
> > > index 87e5be35e5..9bc66d80c4 100644
> > > --- a/xen/common/domain.c
> > > +++ b/xen/common/domain.c
> > > @@ -835,6 +835,8 @@ struct domain *domain_create(domid_t domid,
> > >          flags |= CDF_hardware;
> > >          if ( old_hwdom )
> > >              old_hwdom->cdf &= ~CDF_hardware;
> > > +
> > > +        d->console.input_allowed = true;
> > >      }
> > >
> > >      /* Holding CDF_* internal flags. */
> > > diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> > > index 30701ae0b0..8a0bcff78f 100644
> > > --- a/xen/drivers/char/console.c
> > > +++ b/xen/drivers/char/console.c
> > > @@ -512,9 +512,21 @@ static unsigned int __read_mostly console_rx = 0;
> > >
> > >  struct domain *console_get_domain(void)
> > >  {
> > > +    struct domain *d;
> > > +
> > >      if ( console_rx == 0 )
> > >              return NULL;
> > > -    return rcu_lock_domain_by_id(console_rx - 1);
> > > +
> > > +    d = rcu_lock_domain_by_id(console_rx - 1);
> > > +    if ( !d )
> > > +        return NULL;
> > > +
> > > +    if ( d->console.input_allowed )
> > > +        return d;
> > > +
> > > +    rcu_unlock_domain(d);
> > > +
> > > +    return NULL;
> > 
> > The original idea was to skip over domains that cannot have any input so
> > I don't think we should get in this situation. We could even have an
> > assert.
> > 
> > 
> > >  }
> > >
> > >  void console_put_domain(struct domain *d)
> > > @@ -551,6 +563,10 @@ static void console_switch_input(void)
> > >          if ( d )
> > >          {
> > >              rcu_unlock_domain(d);
> > > +
> > > +            if ( !d->console.input_allowed )
> > > +                break;
> > 
> > shouldn't this be continue instead of break?
> > 
> > 
> > >              console_rx = next_rx;
> > >              printk("*** Serial input to DOM%u", domid);
> > >              break;
> > > diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> > > index 559d201e0c..e91c99a8f3 100644
> > > --- a/xen/include/xen/sched.h
> > > +++ b/xen/include/xen/sched.h
> > > @@ -512,7 +512,7 @@ struct domain
> > >      bool             auto_node_affinity;
> > >      /* Is this guest fully privileged (aka dom0)? */
> > >      bool             is_privileged;
> > > -    /* Can this guest access the Xen console? */
> > > +    /* XSM: permission to use HYPERCALL_console_io hypercall */
> > >      bool             is_console;
> > 
> > While I am in favor of this direction and we certainly need a better way
> > to distinguish domains that can use HYPERCALL_console_io hypercall from
> > others, could we simplify this and just assume that "is_console" implies
> > input_allowed and also set is_console = true in all the same places you
> > are setting input_allowed = true in this patch?
> > 
> > For clarity, I am suggesting:
> > - do not add input_allowed
> > - set is_console = true in domain_vpl011_init, pv_shim_setup_dom, etc.
> > 
> > The only side effect is that we would allow domains with vpl011 to also
> > use console hypercalls but I don't think there is any harm in that?
> > 
> > I don't feel strongly about this, I am just trying to find ways to make
> > things simple. I apologize if it was already discussed during review of
> > one of the previous versions.
> 
> There was feedback on using is_console:
> 
>   https://lore.kernel.org/xen-devel/e899f63b-6182-4b53-9fb4-9a821e75648b@suse.com/
> 
> AFAIU, since XSM is the existing user of is_console, there should be a new
> separate flag to avoid collision with the existing one.

OK, I suspected as much. In that case, it is fine to continue with the
new flag.