linux-kernel - Re: [PATCH RESEND] kvm: make kvm_vcpu_(un)map dependency on CONFIG_HAS

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Date:   Tue, 21 May 2019 07:53:27 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, Radim Krcmar <rkrcmar@...hat.com>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] kvm: make kvm_vcpu_(un)map dependency on
 CONFIG_HAS_IOMEM explicit

On Mon, May 20, 2019 at 07:23:43PM +0200, Paolo Bonzini wrote:
> On 20/05/19 18:44, Michal Kubecek wrote:
> > Recently introduced functions kvm_vcpu_map() and kvm_vcpu_unmap() call
> > memremap() and memunmap() which are only available if HAS_IOMEM is enabled
> > but this dependency is not explicit, so that the build fails with HAS_IOMEM
> > disabled.
> > 
> > As both function are only used on x86 where HAS_IOMEM is always enabled,
> > the easiest fix seems to be to only provide them when HAS_IOMEM is enabled.
> > 
> > Fixes: e45adf665a53 ("KVM: Introduce a new guest mapping API")
> > Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
> > ---
> 
> Thank you very much.  However, it's better if only the memremap part is
> hidden behind CONFIG_HAS_IOMEM.  I'll send a patch tomorrow and have it
> reach Linus at most on Wednesday.

That sounds like a better solution. As I'm not familiar with the code,
I didn't want to risk and suggested the easiest way around.

Michal

> There is actually nothing specific to CONFIG_HAS_IOMEM in them,
> basically the functionality we want is remap_pfn_range but without a
> VMA.  However, it's for a niche use case where KVM guest memory is
> mmap-ed from /dev/mem and it's okay if for now that part remains
> disabled on s390.
> 
> Paolo