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

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Message-ID: <20210610184953.19bed6b4@ibm-vm>
Date:   Thu, 10 Jun 2021 18:49:53 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...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 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

> >   	if (!kvm->arch.pv.stor_var)
> >   		goto out_err;
> >   	return 0;
> >