Re: [PATCH v6 4/7] xen: add bitmap to indicate per-domain state changes

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.01.2025 11:17, Juergen Gross wrote:
> Add a bitmap with one bit per possible domid indicating the respective
> domain has changed its state (created, deleted, dying, crashed,
> shutdown).
> 
> Registering the VIRQ_DOM_EXC event will result in setting the bits for
> all existing domains and resetting all other bits.
> 
> As the usage of this bitmap is tightly coupled with the VIRQ_DOM_EXC
> event, it is meant to be used only by a single consumer in the system,
> just like the VIRQ_DOM_EXC event.
> 
> Resetting a bit will be done in a future patch.
> 
> This information is needed for Xenstore to keep track of all domains.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V2:
> - use DOMID_FIRST_RESERVED instead of DOMID_MASK + 1 (Jan Beulich)
> - use const (Jan Beulich)
> - move call of domain_reset_states() into evtchn_bind_virq() (Jan Beulich)
> - dynamically allocate dom_state_changed bitmap (Jan Beulich)
> V3:
> - use xvzalloc_array() (Jan Beulich)
> - don't rename existing label (Jan Beulich)
> V4:
> - add __read_mostly (Jan Beulich)
> - use __set_bit() (Jan Beulich)

This change looks to have been lost, ...

> - fix error handling in evtchn_bind_virq() (Jan Beulich)
> V5:
> - domain_init_states() may be called only if evtchn_bind_virq() has been
>   called validly (Jan Beulich)
> V6:
> - guard dom_state_changed bitmap with d->event_lock (Jan Beulich)

... without it being mentioned anywhere, and without it becoming clear why
it would have needed undoing.

> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -35,6 +35,7 @@
>  #include <xen/irq.h>
>  #include <xen/argo.h>
>  #include <xen/llc-coloring.h>
> +#include <xen/xvmalloc.h>
>  #include <asm/p2m.h>
>  #include <asm/processor.h>
>  #include <public/sched.h>
> @@ -139,6 +140,51 @@ bool __read_mostly vmtrace_available;
>  
>  bool __read_mostly vpmu_is_available;
>  
> +static unsigned long *__read_mostly dom_state_changed;
> +
> +int domain_init_states(void)
> +{
> +    const struct domain *d;
> +
> +    ASSERT(!dom_state_changed);
> +    ASSERT(rw_is_write_locked(&current->domain->event_lock));

rw_is_write_locked_by_me()?

> +    dom_state_changed = xvzalloc_array(unsigned long,
> +                                       BITS_TO_LONGS(DOMID_FIRST_RESERVED));
> +    if ( !dom_state_changed )
> +        return -ENOMEM;
> +
> +    rcu_read_lock(&domlist_read_lock);
> +
> +    for_each_domain ( d )
> +        set_bit(d->domain_id, dom_state_changed);
> +
> +    rcu_read_unlock(&domlist_read_lock);
> +
> +    return 0;
> +}
> +
> +void domain_deinit_states(const struct domain *d)
> +{
> +    ASSERT(rw_is_write_locked(&d->event_lock));

Again.

Jan