github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-11-07 06:17:02 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

KVM: guest_memfd: Optimize away conversion overheads via dead-code elimination

Browse Source 
Add and use kvm_arch_has_gmem_convert() to guard guest_memfd's invocation
of arch hooks related to converting memory between private and shared, as
only one half of the x86 CoCo duo needs the runtime hooks (any pre-work is
pure overhead for TDX).  At this exact moment, the overhead is negligible,
but that will change when in-place conversion comes along, at which point
to-shared conversions will "need" to find all affected folios prior to
calling into arch code.  In quotes because very technically that work could
be pushed to arch code, but that would bleed guest_memfd details into arch
code and would be far worse than adding yet another kvm_arch_has... hook.

Opportunistically provide the kvm_arch_gmem_make_private() declaration, and
rely on dead-code elimination to eliminate the call to non-existent code
when CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT=n.

Reported-by: Binbin Wu <binbin.wu@linux.intel.com>
Closes: https://lore.kernel.org/all/1ec08cd8-3072-4753-ad5e-cd34956647f8@linux.intel.com
Suggested-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://patch.msgid.link/20260910-gmem-inplace-conversion-v13-1-dd6fbf94f4e1@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-09-10 16:55:27 -07:00
parent 89fbe3de01
commit 54623a16bb
3 changed files with 7 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/x86/include/asm/kvm_host.h
View File

@ -1854,6 +1854,9 @@ enum kvm_intr_type {
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
#define kvm_arch_has_private_mem(kvm) ((kvm)->arch.has_private_mem)
#endif
#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
#define kvm_arch_has_gmem_convert() (!!kvm_x86_ops.gmem_make_private)
#endif
#define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)

3
include/linux/kvm_host.h
View File

@ -2597,9 +2597,10 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm,
}
#endif /* CONFIG_KVM_GUEST_MEMFD */
#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
int kvm_arch_gmem_make_private(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
kvm_pfn_t nr_pages);
#ifndef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
#define kvm_arch_has_gmem_convert() false
#endif
#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE

5
virt/kvm/guest_memfd.c
View File

@ -822,11 +822,10 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
folio_mark_uptodate(folio);
}
#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
if (kvm_gmem_is_private_mem(file_inode(file), index))
if (kvm_arch_has_gmem_convert() &&
kvm_gmem_is_private_mem(file_inode(file), index))
r = kvm_arch_gmem_make_private(kvm, gfn, *pfn,
(kvm_pfn_t)1 << *max_order);
#endif
folio_unlock(folio);
folio_put(folio);