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Mon, 07 Sep 2026 14:43:29 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (smtpav03.fra02v.mail.ibm.com [10.20.54.102]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 687EhPqC45351172 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 7 Sep 2026 14:43:25 GMT Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8BCB52004B; Mon, 7 Sep 2026 14:43:25 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3CC3820043; Mon, 7 Sep 2026 14:43:25 +0000 (GMT) Received: from [9.87.132.113] (unknown [9.87.132.113]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 7 Sep 2026 14:43:25 +0000 (GMT) Message-ID: <42c74898-939c-4253-8e36-3502c5f7b277@linux.ibm.com> Date: Mon, 7 Sep 2026 16:43:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] KVM: s390: Replace get_zeroed_page() with kzalloc() for sie_page2 and CMMA To: "Mike Rapoport (Microsoft)" , Christian Borntraeger , Claudio Imbrenda Cc: Alexander Gordeev , David Hildenbrand , Heiko Carstens , Sven Schnelle , Vasily Gorbik , Vlastimil Babka , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org References: <20260906-s390-kvm-v2-0-2cf6434e6646@kernel.org> <20260906-s390-kvm-v2-4-2cf6434e6646@kernel.org> Content-Language: en-US From: Janosch Frank Autocrypt: addr=frankja@linux.ibm.com; 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Both are passed to the hardware as physical > addresses and must be page aligned. > > kmalloc() guarantees that a power of two sized allocation is aligned to > its size, so a PAGE_SIZE allocation is page aligned as well. > > These buffers can be allocated with kmalloc() as there's nothing special > about them to go directly to the page allocator. > > kmalloc() provides a better API that does not require ugly casts and > kfree() does not need to know the size of the freed object. > > Performance difference between kmalloc() and __get_free_pages() is not > measurable as both allocators take an object/page from a per-CPU list for > fast path allocations. > > For the slow path the performance is anyway determined by the amount of > reclaim involved rather than by what allocator is used. > > The sie_page allocated in kvm_arch_vcpu_create() is left alone because it > is mapped to userspace with virt_to_page() in kvm_arch_vcpu_fault() and > therefore really needs a struct page. > > The SIE hardware stores the offset of the next CBR entry in the low bits > of cbrlo, so mask them out before converting cbrlo back to a virtual > address. free_page() did not care, kfree() needs the address kzalloc() > returned. > > Replace use of get_zeroed_page() with kzalloc() and free_page() with > kfree(). > > Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com > Assisted-by: copilot:claude-opus > Signed-off-by: Mike Rapoport (Microsoft) Reviewed-by: Janosch Frank