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.

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

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
>

On 2023/5/31 17:53, Baoquan He wrote:
> 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>

OK, I will update the log and add Acked-by in v2.

> 
>>
>> 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
>>
> 
> .
> 

-- 
Regards,
  Zhen Lei