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

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Date:   Mon, 20 May 2019 19:23:43 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Michal Kubecek <mkubecek@...e.cz>, kvm@...r.kernel.org
Cc:     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 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.

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