Re: [PATCH v1 07/11] fs/proc/vmcore: introduce PROC_VMCORE_DEVICE_RAM to detect device RAM ranges in 2nd kernel

Baoquan He
2024-11-22T07:31:32Z

On 10/25/24 at 05:11pm, David Hildenbrand wrote:
......snip...
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 3e90416ee54e..c332a9a4920b 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -69,6 +69,8 @@ static LIST_HEAD(vmcore_cb_list);
> /* Whether the vmcore has been opened once. */
> static bool vmcore_opened;
>
> +static void vmcore_process_device_ram(struct vmcore_cb *cb);
> +
> void register_vmcore_cb(struct vmcore_cb *cb)
> {
> INIT_LIST_HEAD(&cb->next);
> @@ -80,6 +82,8 @@ void register_vmcore_cb(struct vmcore_cb *cb)
> */
> if (vmcore_opened)
> pr_warn_once("Unexpected vmcore callback registration\n");
> + else if (cb->get_device_ram)
> + vmcore_process_device_ram(cb);

Global variable 'vmcore_opened' is used to indicate if /proc/vmcore is
opened. With &vmcore_mutex, we don't need to worry about concurrent
opening and modification. However, if people just open /proc/vmcore and
close it after checking, then s390 will miss the vmcore dumping, is it
acceptable?

> mutex_unlock(&vmcore_mutex);
> }
> EXPORT_SYMBOL_GPL(register_vmcore_cb);
> @@ -1511,6 +1515,158 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
......
> +
> +static void vmcore_process_device_ram(struct vmcore_cb *cb)
> +{
> + unsigned char *e_ident = (unsigned char *)elfcorebuf;
> + struct vmcore_mem_node *first, *m;
> + LIST_HEAD(list);
> + int count;
> +
> + if (cb->get_device_ram(cb, &list)) {
> + pr_err("Kdump: obtaining device ram ranges failed\n");
> + return;
> + }
> + count = list_count_nodes(&list);
> + if (!count)
> + return;
> +
> + /* We only support Elf64 dumps for now. */
> + if (WARN_ON_ONCE(e_ident[EI_CLASS] != ELFCLASS64)) {
> + pr_err("Kdump: device ram ranges only support Elf64\n");
> + goto out_free;
> + }

Only supporting Elf64 dumps seems to be a basic checking, do we need
to put it at the beginning of function? Otherwise, we spend efforts to
call cb->get_device_ram(), then fail.

> +
> + /*
> + * For some reason these ranges are already know? Might happen
> + * with unusual register->unregister->register sequences; we'll simply
> + * sanity check using the first range.
> + */
> + first = list_first_entry(&list, struct vmcore_mem_node, list);
> + list_for_each_entry(m, &vmcore_list, list) {
> + unsigned long long m_end = m->paddr + m->size;
> + unsigned long long first_end = first->paddr + first->size;
> +
> + if (first->paddr < m_end && m->paddr < first_end)
> + goto out_free;
> + }
> +
> + /* If adding the mem nodes succeeds, they must not be freed. */
> + if (!vmcore_add_device_ram_elf64(&list, count))
> + return;
> +out_free:
> + vmcore_free_mem_nodes(&list);
> +}
> +#else /* !CONFIG_PROC_VMCORE_DEVICE_RAM */
> +static void vmcore_process_device_ram(struct vmcore_cb *cb)
> +{
> +}
> +#endif /* CONFIG_PROC_VMCORE_DEVICE_RAM */
> +
> /* Free all dumps in vmcore device dump list */
> static void vmcore_free_device_dumps(void)
> {
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index 722dbcff7371..8e581a053d7f 100644
> --- a/include/linux/crash_dump.h
> +++ b/include/linux/crash_dump.h