On 22.01.25 16:27, Fuad Tabba wrote:
Add support for mmap() and fault() for guest_memfd in the host
for VMs that support in place conversion between shared and
private.
> To that end, this patch adds the ability to check> whether the
architecture has that support, and only allows mmap()
if that's the case.
> > Additionally, this is gated with a new configuration option,
CONFIG_KVM_GMEM_MAPPABLE.
> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 +
include/linux/kvm_host.h | 11 +++++
virt/kvm/Kconfig | 4 ++
virt/kvm/guest_memfd.c | 71 +++++++++++++++++++++++++++++++++
4 files changed, 88 insertions(+)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index e159e44a6a1b..c0e149bc1d79 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2206,6 +2206,8 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
#define kvm_arch_has_private_mem(kvm) false
#endif
+#define kvm_arch_private_mem_inplace(kvm) false
+
#define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)
static inline u16 kvm_read_ldt(void)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 401439bb21e3..ebca0ab4c5e2 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -717,6 +717,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm)
}
#endif
+/*
+ * Arch code must define kvm_arch_private_mem_inplace if support for private
+ * memory is enabled it supports in-place conversion between shared and private.
+ */
+#if !defined(kvm_arch_private_mem_inplace) && !IS_ENABLED(CONFIG_KVM_PRIVATE_MEM)
+static inline bool kvm_arch_private_mem_inplace(struct kvm *kvm)
I assume right now this would rather indicate "support for shared
(mappable) memory in guest_memfd".
Maybe there is a better way to express that :)
kvm_arch_gmem_supports_shared_mem ?
The in-place conversion is (at least to me) implied with support for
shared memory.
+
#ifndef kvm_arch_has_readonly_mem
static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm)
{
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 54e959e7d68f..59400fd8f539 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -124,3 +124,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE
config HAVE_KVM_ARCH_GMEM_INVALIDATE
bool
depends on KVM_PRIVATE_MEM
+
+config KVM_GMEM_MAPPABLE
+ select KVM_PRIVATE_MEM
Easier to grasp might be:
KVM_GMEM_MAPPABLE -> KVM_GMEM_SHARED_MEM
Support for "shared" memory kind of imply mmap support (otherwise, how
to make use of it :) ),
(KVM_PRIVATE_MEM -> KVM_GMEM might also make sense, but it's a different
discussion)
+ bool
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 47a9f68f7b24..9ee162bf6bde 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -307,7 +307,78 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
return gfn - slot->base_gfn + slot->gmem.pgoff;
}
+#ifdef CONFIG_KVM_GMEM_MAPPABLE
+static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf)
+{
+ struct inode *inode = file_inode(vmf->vma->vm_file);
+ struct folio *folio;
+ vm_fault_t ret = VM_FAULT_LOCKED;
+
+ filemap_invalidate_lock_shared(inode->i_mapping);
+
+ folio = kvm_gmem_get_folio(inode, vmf->pgoff);
Would the idea be later that kvm_gmem_get_folio() would fail on private
memory, or do you envision other checks in this code here in the future?
--
Cheers,
David / dhildenb
