linux-kernel - Re: [RFC PATCH v12 14/33] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory

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Date:   Fri, 15 Sep 2023 14:11:18 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Huacai Chen <chenhuacai@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anup Patel <anup@...infault.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, <kvm@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
        <linux-mips@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
        <kvm-riscv@...ts.infradead.org>, <linux-riscv@...ts.infradead.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Fuad Tabba <tabba@...gle.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Anish Moorthy <amoorthy@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Xu Yilun <yilun.xu@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Maciej Szmigiero <mail@...iej.szmigiero.name>,
        David Hildenbrand <david@...hat.com>,
        Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>,
        Wang <wei.w.wang@...el.com>,
        "Liam Merwick" <liam.merwick@...cle.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC PATCH v12 14/33] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl()
 for guest-specific backing memory

On Wed, Sep 13, 2023 at 06:55:12PM -0700, Sean Christopherson wrote:
> +static struct folio *kvm_gmem_get_folio(struct file *file, pgoff_t index)
> +{
> +	struct folio *folio;
> +
> +	/* TODO: Support huge pages. */
> +	folio = filemap_grab_folio(file->f_mapping, index);
> +	if (IS_ERR_OR_NULL(folio))
> +		return NULL;
> +
> +	/*
> +	 * Use the up-to-date flag to track whether or not the memory has been
> +	 * zeroed before being handed off to the guest.  There is no backing
> +	 * storage for the memory, so the folio will remain up-to-date until
> +	 * it's removed.
> +	 *
> +	 * TODO: Skip clearing pages when trusted firmware will do it when
> +	 * assigning memory to the guest.
> +	 */
> +	if (!folio_test_uptodate(folio)) {
> +		unsigned long nr_pages = folio_nr_pages(folio);
> +		unsigned long i;
> +
> +		for (i = 0; i < nr_pages; i++)
> +			clear_highpage(folio_page(folio, i));
> +
> +		folio_mark_uptodate(folio);
> +	}
> +
> +	/*
> +	 * Ignore accessed, referenced, and dirty flags.  The memory is
> +	 * unevictable and there is no storage to write back to.
> +	 */
> +	return folio;
> +}
If VFIO wants to map a private page, is it required to call this function for PFN?