linux-kernel - Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared memory are mixed

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Date:   Fri, 13 Jan 2023 23:16:27 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
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        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
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        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 7/9] KVM: Update lpage info when private/shared
 memory are mixed

On Fri, Dec 02, 2022, Chao Peng wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a07380f8d3c..5aefcff614d2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12362,6 +12362,8 @@ static int kvm_alloc_memslot_metadata(struct kvm *kvm,
>  		if ((slot->base_gfn + npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
>  			linfo[lpages - 1].disallow_lpage = 1;
>  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
> +		if (kvm_slot_can_be_private(slot))
> +			ugfn |= slot->restricted_offset >> PAGE_SHIFT;
>  		/*
>  		 * If the gfn and userspace address are not aligned wrt each
>  		 * other, disable large page support for this slot.

Forgot to talk about the bug.  This code needs to handle the scenario where a
memslot is created with existing, non-uniform attributes.  It might be a bit ugly
(I didn't even try to write the code), but it's definitely possible, and since
memslot updates are already slow I think it's best to handle things here.

In the meantime, I added this so we don't forget to fix it before merging.

#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
	pr_crit_once("FIXME: Walk the memory attributes of the slot and set the mixed status appropriately");
#endif