linux-kernel - Re: [PATCH 3/3] s390/mm: Define arch_get_mappable

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Message-ID: <04da0f9c-d50e-7729-5e4c-b0dc4e76d608@arm.com>
Date:   Thu, 10 Dec 2020 09:48:11 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, david@...hat.com,
        catalin.marinas@....com, linux-arm-kernel@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 3/3] s390/mm: Define arch_get_mappable_range()



On 12/9/20 8:27 PM, Heiko Carstens wrote:
> On Wed, Dec 09, 2020 at 08:07:04AM +0530, Anshuman Khandual wrote:
>>>> +	if (seg->end + 1 > VMEM_MAX_PHYS || seg->end + 1 < seg->start_addr) {
>>>> +		rc = -ERANGE;
>>>> +		goto out_resource;
>>>> +	}
>>>> +
> ...
>>>> +struct range arch_get_mappable_range(void)
>>>> +{
>>>> +	struct range memhp_range;
>>>> +
>>>> +	memhp_range.start = 0;
>>>> +	memhp_range.end =  VMEM_MAX_PHYS;
>>>> +	return memhp_range;
>>>> +}
>>>> +
>>>>  int arch_add_memory(int nid, u64 start, u64 size,
>>>>  		    struct mhp_params *params)
>>>>  {
>>>> @@ -291,6 +300,7 @@ int arch_add_memory(int nid, u64 start, u64 size,
>>>>  	if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
>>>>  		return -EINVAL;
>>>>  
>>>> +	VM_BUG_ON(!memhp_range_allowed(start, size, 1));
>>>>  	rc = vmem_add_mapping(start, size);
>>>>  	if (rc)
>>> Is there a reason why you added the memhp_range_allowed() check call
>>> to arch_add_memory() instead of vmem_add_mapping()? If you would do
>>
>> As I had mentioned previously, memhp_range_allowed() is available with
>> CONFIG_MEMORY_HOTPLUG but vmem_add_mapping() is always available. Hence
>> there will be a build failure in vmem_add_mapping() for the range check
>> memhp_range_allowed() without memory hotplug enabled.
>>
>>> that, then the extra code in __segment_load() wouldn't be
>>> required.
>>> Even though the error message from memhp_range_allowed() might be
>>> highly confusing.
>>
>> Alternatively leaving __segment_load() and vmem_add_memory() unchanged
>> will create three range checks i.e two memhp_range_allowed() and the
>> existing VMEM_MAX_PHYS check in vmem_add_mapping() on all the hotplug
>> paths, which is not optimal.
> 
> Ah, sorry. I didn't follow this discussion too closely. I just thought
> my point of view would be clear: let's not have two different ways to
> check for the same thing which must be kept in sync.
> Therefore I was wondering why this next version is still doing
> that. Please find a way to solve this.

The following change is after the current series and should work with
and without memory hotplug enabled. There will be just a single place
i.e vmem_get_max_addr() to update in case the maximum address changes
from VMEM_MAX_PHYS to something else later.

diff --git a/arch/s390/include/asm/sections.h b/arch/s390/include/asm/sections.h
index 0c21514..2da496f 100644
--- a/arch/s390/include/asm/sections.h
+++ b/arch/s390/include/asm/sections.h
@@ -16,6 +16,7 @@ static inline int arch_is_kernel_initmem_freed(unsigned long addr)
 	       addr < (unsigned long)__init_end;
 }
 
+unsigned long vmem_get_max_addr(void);
 /*
  * .boot.data section contains variables "shared" between the decompressor and
  * the decompressed kernel. The decompressor will store values in them, and
diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c
index cc055a7..1bddd6f 100644
--- a/arch/s390/mm/extmem.c
+++ b/arch/s390/mm/extmem.c
@@ -28,6 +28,7 @@
 #include <asm/extmem.h>
 #include <asm/cpcmd.h>
 #include <asm/setup.h>
+#include <asm/sections.h>
 
 #define DCSS_PURGESEG   0x08
 #define DCSS_LOADSHRX	0x20
@@ -287,6 +288,13 @@ segment_overlaps_others (struct dcss_segment *seg)
 	return 0;
 }
 
+static bool segment_outside_range(struct dcss_segment *seg)
+{
+	unsigned long max_addr = vmem_get_max_addr();
+
+	return (seg->end + 1 > max_addr || seg->end + 1 < seg->start_addr);
+}
+
 /*
  * real segment loading function, called from segment_load
  */
@@ -337,7 +345,7 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
 		goto out_free_resource;
 	}
 
-	if (seg->end + 1 > VMEM_MAX_PHYS || seg->end + 1 < seg->start_addr) {
+	if (segment_outside_range(seg)) {
 		rc = -ERANGE;
 		goto out_resource;
 	}
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 64937ba..5c6ee9f 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -283,7 +283,7 @@ struct range arch_get_mappable_range(void)
 	struct range memhp_range;
 
 	memhp_range.start = 0;
-	memhp_range.end =  VMEM_MAX_PHYS;
+	memhp_range.end =  vmem_get_max_addr();
 	return memhp_range;
 }
 
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 749eab4..6044e85 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -532,6 +532,11 @@ void vmem_remove_mapping(unsigned long start, unsigned long size)
 	mutex_unlock(&vmem_mutex);
 }
 
+unsigned long vmem_get_max_addr(void)
+{
+        return VMEM_MAX_PHYS;
+}
+
 int vmem_add_mapping(unsigned long start, unsigned long size)
 {
 	int ret;
-- 
2.7.4