linux-kernel - [PATCH v5 08/13] KVM: Use memfile_pfn_ops to obtain pfn for private pages

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Date:   Thu, 10 Mar 2022 22:09:06 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, qemu-devel@...gnu.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        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>,
        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>,
        Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com
Subject: [PATCH v5 08/13] KVM: Use memfile_pfn_ops to obtain pfn for private pages

Private pages are not mmap-ed into userspace so can not reply on
get_user_pages() to obtain the pfn. Instead we add a memfile_pfn_ops
pointer pfn_ops in each private memslot and use it to obtain the pfn
for a gfn. To do that, KVM should convert the gfn to the offset into
the fd and then call get_lock_pfn callback. Once KVM completes its job
it should call put_unlock_pfn to unlock the pfn. Note the pfn(page) is
locked between get_lock_pfn/put_unlock_pfn to ensure pfn is valid when
KVM uses it to establish the mapping in the secondary MMU page table.

The pfn_ops is initialized via memfile_register_notifier from the memory
backing store that provided the private_fd.

Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
---
 arch/x86/kvm/Kconfig     |  1 +
 include/linux/kvm_host.h | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index e3cbd7706136..ca7b2a6a452a 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -48,6 +48,7 @@ config KVM
 	select SRCU
 	select INTERVAL_TREE
 	select HAVE_KVM_PM_NOTIFIER if PM
+	select MEMFILE_NOTIFIER
 	help
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c92c70174248..6e1d770d6bf8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -44,6 +44,7 @@
 
 #include <asm/kvm_host.h>
 #include <linux/kvm_dirty_ring.h>
+#include <linux/memfile_notifier.h>
 
 #ifndef KVM_MAX_VCPU_IDS
 #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
@@ -565,6 +566,7 @@ struct kvm_memory_slot {
 	u16 as_id;
 	struct file *private_file;
 	loff_t private_offset;
+	struct memfile_pfn_ops *pfn_ops;
 };
 
 static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)
@@ -915,6 +917,7 @@ static inline void kvm_irqfd_exit(void)
 {
 }
 #endif
+
 int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 		  struct module *module);
 void kvm_exit(void);
@@ -2217,4 +2220,34 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
 /* Max number of entries allowed for each kvm dirty ring */
 #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
 
+#ifdef CONFIG_MEMFILE_NOTIFIER
+static inline long kvm_memfile_get_pfn(struct kvm_memory_slot *slot, gfn_t gfn,
+				       int *order)
+{
+	pgoff_t index = gfn - slot->base_gfn +
+			(slot->private_offset >> PAGE_SHIFT);
+
+	return slot->pfn_ops->get_lock_pfn(file_inode(slot->private_file),
+					   index, order);
+}
+
+static inline void kvm_memfile_put_pfn(struct kvm_memory_slot *slot,
+				       kvm_pfn_t pfn)
+{
+	slot->pfn_ops->put_unlock_pfn(pfn);
+}
+
+#else
+static inline long kvm_memfile_get_pfn(struct kvm_memory_slot *slot, gfn_t gfn,
+				       int *order)
+{
+	return -1;
+}
+
+static inline void kvm_memfile_put_pfn(struct kvm_memory_slot *slot,
+				       kvm_pfn_t pfn)
+{
+}
+#endif /* CONFIG_MEMFILE_NOTIFIER */
+
 #endif
-- 
2.17.1