linux-kernel - Re: [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in kvm_arch_commit_memory

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Message-ID: <YaVALTZbutlVPz8k@google.com>
Date:   Mon, 29 Nov 2021 21:03:41 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Igor Mammedov <imammedo@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in
 kvm_arch_commit_memory_region()

On Fri, Nov 26, 2021, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>
> 
> With kvm->nr_memslot_pages capped at ULONG_MAX we can't safely multiply it
> by KVM_PERMILLE_MMU_PAGES (20) since this operation can possibly overflow
> an unsigned long variable.
> 
> Rewrite this "* 20 / 1000" operation as "/ 50" instead to avoid such
> overflow.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>