Re: [PATCH -next v2 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

[Baoquan He <bhe@redhat.com>]

On 03/30/23 at 09:40pm, chenjiahao (C) wrote:
......
> Agreed, I will clean this up later in next version.
> > > +		if (ret || !crash_size)
> > > +			return;
> > > +
> > > +		/*
> > > +		 * crashkernel=Y,low is valid only when crashkernel=X,high
> > > +		 * is passed and high memory is reserved successful.
> > > +		 */
> > > +		ret = parse_crashkernel_low(boot_command_line, 0, &crash_low_size, &crash_base);
> > > +		if (ret == -ENOENT)
> > > +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> > > +		else if (ret)
> > > +			return;
> > > +
> > > +		search_start = dma32_phys_limit;
> > > +	} else if (ret || !crash_size) {
> > > +		/* Invalid argument value specified */
> > >   		return;
> > > +	}
> > >   	crash_size = PAGE_ALIGN(crash_size);
> > > @@ -1201,16 +1246,26 @@ static void __init reserve_crashkernel(void)
> > >   	 */
> > >   	crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
> > >   					       search_start,
> > > -					       min(search_end, (unsigned long) SZ_4G));
> > > +					       min(search_end, (unsigned long)dma32_phys_limit));
> > >   	if (crash_base == 0) {
> > The above conditional check isn't right. If crashkernel=size@offset
> > specified, the reservation failure won't trigger retry. This seems to be
> > originally introduced by old commit, while this need be fixed firstly.
> 
> Just a little curious about the rule to cope with this specific case. If
> "crashkernel=size@offset" was passed
> 
> but reserve failed, should try again to allocate in high memory, regardless
> the specified size@offset,
> 
> or just throw a warning and return? Since I noticed the current logic here
> on Arm64 is to check if !fixed_base first

Yeah, we need mark the "crashkernel=size@offset" case and avoid to
retry. Because you won't succeed if  memblock has already failed to
reserve an unavailable memory region, retry is meaningless. This has
been done in x86, arm64.