From: Paolo Bonzini <pbonzini@redhat.com>
Date: Sat, 9 Mar 2024 16:48:35 +0000 (-0500)
Subject: Merge tag 'kvm-x86-guest_memfd_fixes-6.8' of https://github.com/kvm-x86/linux into... 
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=7d8942d8e73843de35b3737b8be50f8fef6796bb;p=linux.git

Merge tag 'kvm-x86-guest_memfd_fixes-6.8' of https://github.com/kvm-x86/linux into HEAD

KVM GUEST_MEMFD fixes for 6.8:

 - Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY to
   avoid creating ABI that KVM can't sanely support.

 - Update documentation for KVM_SW_PROTECTED_VM to make it abundantly
   clear that such VMs are purely a development and testing vehicle, and
   come with zero guarantees.

 - Limit KVM_SW_PROTECTED_VM guests to the TDP MMU, as the long term plan
   is to support confidential VMs with deterministic private memory (SNP
   and TDX) only in the TDP MMU.

 - Fix a bug in a GUEST_MEMFD negative test that resulted in false passes
   when verifying that KVM_MEM_GUEST_MEMFD memslots can't be dirty logged.
---

7d8942d8e73843de35b3737b8be50f8fef6796bb
diff --cc virt/kvm/kvm_main.c
index ff588677beb7d,0f50960b0e3a8..054d20ec61b97
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@@ -1614,8 -1614,14 +1614,14 @@@ static int check_memory_region_flags(st
  	if (mem->flags & KVM_MEM_GUEST_MEMFD)
  		valid_flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
  
 -#ifdef __KVM_HAVE_READONLY_MEM
 +#ifdef CONFIG_HAVE_KVM_READONLY_MEM
- 	valid_flags |= KVM_MEM_READONLY;
+ 	/*
+ 	 * GUEST_MEMFD is incompatible with read-only memslots, as writes to
+ 	 * read-only memslots have emulated MMIO, not page fault, semantics,
+ 	 * and KVM doesn't allow emulated MMIO for private memory.
+ 	 */
+ 	if (!(mem->flags & KVM_MEM_GUEST_MEMFD))
+ 		valid_flags |= KVM_MEM_READONLY;
  #endif
  
  	if (mem->flags & ~valid_flags)