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Date:   Wed, 31 May 2023 17:53:34 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Zhen Lei <thunder.leizhen@huawei.com>
Cc:     Eric Biederman <ebiederm@xmission.com>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        Michael Holzheu <holzheu@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 6/6] kexec: enable kexec_crash_size to support two crash
 kernel regions
Message-ID: <ZHcY/jsExa8t7hJW@MiWiFi-R3L-srv>
References: <20230527123439.772-1-thunder.leizhen@huawei.com>
 <20230527123439.772-7-thunder.leizhen@huawei.com>
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In-Reply-To: <20230527123439.772-7-thunder.leizhen@huawei.com>
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On 05/27/23 at 08:34pm, Zhen Lei wrote:
> The crashk_low_res should be considered by /sys/kernel/kexec_crash_size
> to support two crash kernel regions. Since crashk_res manages the memory
> with high address and crashk_low_res manages the memory with low address,
> crashk_low_res is shrunken only when all crashk_res is shrunken. And
> because when there is only one crash kernel region, crashk_res is always
> used. Therefore, if all crashk_res is shrunken and crashk_low_res still
> exists, swap them.

This looks good, otherwise someone else won't stop attempting to add
support of crashk_low_res shrinking. Not sure if this will bring corner
case issue in testing, let's see. For the patch log, I tried to
rephrase, feel free to refer to.

=====
The crashk_low_res should be considered by /sys/kernel/kexec_crash_size
to support two crash kernel regions shrinking if existing.

While doing it, crashk_low_res will only be shrunk when the entire
crashk_res is empty; and if the crashk_res is empty and crahk_low_res
is not, change crashk_low_res to be crashk_res.
=====

With the log updated, you can add:

Acked-by: Baoquan He <bhe@redhat.com>

> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> ---
>  kernel/kexec_core.c | 43 ++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index e82bc6d6634136a..c1d50f6566300d9 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1091,6 +1091,11 @@ __bpf_kfunc void crash_kexec(struct pt_regs *regs)
>  	}
>  }
>  
> +static inline resource_size_t crash_resource_size(const struct resource *res)
> +{
> +	return !res->end ? 0 : resource_size(res);
> +}
> +
>  ssize_t crash_get_memory_size(void)
>  {
>  	ssize_t size = 0;
> @@ -1098,8 +1103,8 @@ ssize_t crash_get_memory_size(void)
>  	if (!kexec_trylock())
>  		return -EBUSY;
>  
> -	if (crashk_res.end != crashk_res.start)
> -		size = resource_size(&crashk_res);
> +	size += crash_resource_size(&crashk_res);
> +	size += crash_resource_size(&crashk_low_res);
>  
>  	kexec_unlock();
>  	return size;
> @@ -1135,7 +1140,7 @@ int __crash_shrink_memory(struct resource *old_res, unsigned long new_size)
>  int crash_shrink_memory(unsigned long new_size)
>  {
>  	int ret = 0;
> -	unsigned long old_size;
> +	unsigned long old_size, low_size;
>  
>  	if (!kexec_trylock())
>  		return -EBUSY;
> @@ -1144,14 +1149,42 @@ int crash_shrink_memory(unsigned long new_size)
>  		ret = -ENOENT;
>  		goto unlock;
>  	}
> -	old_size = !crashk_res.end ? 0 : resource_size(&crashk_res);
> +
> +	low_size = crash_resource_size(&crashk_low_res);
> +	old_size = crash_resource_size(&crashk_res) + low_size;
>  	new_size = roundup(new_size, KEXEC_CRASH_MEM_ALIGN);
>  	if (new_size >= old_size) {
>  		ret = (new_size == old_size) ? 0 : -EINVAL;
>  		goto unlock;
>  	}
>  
> -	ret = __crash_shrink_memory(&crashk_res, new_size);
> +	/*
> +	 * (low_size > new_size) implies that low_size is greater than zero.
> +	 * This also means that if low_size is zero, the else branch is taken.
> +	 *
> +	 * If low_size is greater than 0, (low_size > new_size) indicates that
> +	 * crashk_low_res also needs to be shrunken. Otherwise, only crashk_res
> +	 * needs to be shrunken.
> +	 */
> +	if (low_size > new_size) {
> +		ret = __crash_shrink_memory(&crashk_res, 0);
> +		if (ret)
> +			goto unlock;
> +
> +		ret = __crash_shrink_memory(&crashk_low_res, new_size);
> +	} else {
> +		ret = __crash_shrink_memory(&crashk_res, new_size - low_size);
> +	}
> +
> +	/* Swap crashk_res and crashk_low_res if needed */
> +	if (!crashk_res.end && crashk_low_res.end) {
> +		crashk_res.start = crashk_low_res.start;
> +		crashk_res.end   = crashk_low_res.end;
> +		release_resource(&crashk_low_res);
> +		crashk_low_res.start = 0;
> +		crashk_low_res.end   = 0;
> +		insert_resource(&iomem_resource, &crashk_res);
> +	}
>  
>  unlock:
>  	kexec_unlock();
> -- 
> 2.25.1
>