linux-kernel - Re: [PATCH v3 2/2] KVM: s390: fix for hugepage vmalloc

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Date:   Thu, 10 Jun 2021 18:52:18 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, frankja@...ux.ibm.com,
        cohuck@...hat.com, david@...hat.com, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Uladzislau Rezki <urezki@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v3 2/2] KVM: s390: fix for hugepage vmalloc



On 10.06.21 18:49, Claudio Imbrenda wrote:
> On Thu, 10 Jun 2021 17:56:58 +0200
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
>> On 10.06.21 17:42, Claudio Imbrenda wrote:
>>> The Create Secure Configuration Ultravisor Call does not support
>>> using large pages for the virtual memory area. This is a hardware
>>> limitation.
>>>
>>> This patch replaces the vzalloc call with an almost equivalent call
>>> to the newly introduced vmalloc_no_huge function, which guarantees
>>> that only small pages will be used for the backing.
>>>
>>> The new call will not clear the allocated memory, but that has never
>>> been an actual requirement.
> 
> ^ here
> 
>>> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
>>> Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Cc: Nicholas Piggin <npiggin@...il.com>
>>> Cc: Uladzislau Rezki (Sony) <urezki@...il.com>
>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: Ingo Molnar <mingo@...hat.com>
>>> Cc: David Rientjes <rientjes@...gle.com>
>>> Cc: Christoph Hellwig <hch@...radead.org>
>>> ---
>>>    arch/s390/kvm/pv.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
>>> index 813b6e93dc83..ad7c6d7cc90b 100644
>>> --- a/arch/s390/kvm/pv.c
>>> +++ b/arch/s390/kvm/pv.c
>>> @@ -140,7 +140,7 @@ static int kvm_s390_pv_alloc_vm(struct kvm *kvm)
>>>    	/* Allocate variable storage */
>>>    	vlen = ALIGN(virt * ((npages * PAGE_SIZE) / HPAGE_SIZE),
>>> PAGE_SIZE); vlen += uv_info.guest_virt_base_stor_len;
>>> -	kvm->arch.pv.stor_var = vzalloc(vlen);
>>> +	kvm->arch.pv.stor_var = vmalloc_no_huge(vlen);
>>
>> dont we need a memset now?
> 
> no, as explained above

Makes sense.

Acked-by: Christian Borntraeger <borntraeger@...ibm.com>