linux-kernel - Re: [PATCH v2 3/5] KVM: Add a dedicated API for setting KVM-internal memslots

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Message-Id: <D76ZBOXNTIGF.3D0BBERDWTY2C@linux.ibm.com>
Date: Mon, 20 Jan 2025 15:44:33 +0100
From: "Christoph Schlameuss" <schlameuss@...ux.ibm.com>
To: "Sean Christopherson" <seanjc@...gle.com>
Cc: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Paolo Bonzini"
 <pbonzini@...hat.com>,
        "Tao Su" <tao1.su@...ux.intel.com>,
        "Claudio
 Imbrenda" <imbrenda@...ux.ibm.com>,
        "Christian Borntraeger"
 <borntraeger@...ibm.com>,
        "Xiaoyao Li" <xiaoyao.li@...el.com>
Subject: Re: [PATCH v2 3/5] KVM: Add a dedicated API for setting
 KVM-internal memslots

On Sat Jan 11, 2025 at 1:20 AM CET, Sean Christopherson wrote:
> Add a dedicated API for setting internal memslots, and have it explicitly
> disallow setting userspace memslots.  Setting a userspace memslots without
> a direct command from userspace would result in all manner of issues.
>
> No functional change intended.
>
> Cc: Tao Su <tao1.su@...ux.intel.com>
> Cc: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ibm.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c       |  2 +-
>  include/linux/kvm_host.h |  4 ++--
>  virt/kvm/kvm_main.c      | 15 ++++++++++++---
>  3 files changed, 15 insertions(+), 6 deletions(-)

[...]

> +int kvm_set_internal_memslot(struct kvm *kvm,
> +			     const struct kvm_userspace_memory_region2 *mem)
> +{
> +	if (WARN_ON_ONCE(mem->slot < KVM_USER_MEM_SLOTS))
> +		return -EINVAL;
> +

Looking at Claudios changes I found that this is missing to acquire the
slots_lock here.

guard(mutex)(&kvm->slots_lock);

> +	return __kvm_set_memory_region(kvm, mem);
> +}
> +EXPORT_SYMBOL_GPL(kvm_set_internal_memslot);
>  
>  static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
>  					  struct kvm_userspace_memory_region2 *mem)