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KVM nested SVM changes for 7.1 (with one common x86 fix)

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- To minimize the probability of corrupting guest state, defer KVM's
    non-architectural delivery of exception payloads (e.g. CR2 and DR6) until
    consumption of the payload is imminent, and force delivery of the payload
    in all paths where userspace saves relevant state.
 
  - Use vcpu->arch.cr2 when updating vmcb12's CR2 on nested #VMEXIT to fix a
    bug where L2's CR2 can get corrupted after a save/restore, e.g. if the VM
    is migrated while L2 is faulting in memory.
 
  - Fix a class of nSVM bugs where some fields written by the CPU are not
    synchronized from vmcb02 to cached vmcb12 after VMRUN, and so are not
    up-to-date when saved by KVM_GET_NESTED_STATE.
 
  - Fix a class of bugs where the ordering between KVM_SET_NESTED_STATE and
    KVM_SET_{S}REGS could cause vmcb02 to be incorrectly initialized after
    save+restore.
 
  - Add a variety of missing nSVM consistency checks.
 
  - Fix several bugs where KVM failed to correctly update VMCB fields on nested
    #VMEXIT.
 
  - Fix several bugs where KVM failed to correctly synthesize #UD or #GP for
    SVM-related instructions.
 
  - Add support for save+restore of virtualized LBRs (on SVM).
 
  - Refactor various helpers and macros to improve clarity and (hopefully) make
    the code easier to maintain.
 
  - Aggressively sanitize fields when copying from vmcb12 to guard against
    unintentionally allowing L1 to utilize yet-to-be-defined features.
 
  - Fix several bugs where KVM botched rAX legality checks when emulating SVM
    instructions.  Note, KVM is still flawed in that KVM doesn't address size
    prefix overrides for 64-bit guests; this should probably be documented as a
    KVM erratum.
 
  - Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails instead of
    somewhat arbitrarily synthesizing #GP (i.e. don't bastardize AMD's already-
    sketchy behavior of generating #GP if for "unsupported" addresses).
 
  - Cache all used vmcb12 fields to further harden against TOCTOU bugs.
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Merge tag 'kvm-x86-nested-7.1' of https://github.com/kvm-x86/linux into HEAD

KVM nested SVM changes for 7.1 (with one common x86 fix)

 - To minimize the probability of corrupting guest state, defer KVM's
   non-architectural delivery of exception payloads (e.g. CR2 and DR6) until
   consumption of the payload is imminent, and force delivery of the payload
   in all paths where userspace saves relevant state.

 - Use vcpu->arch.cr2 when updating vmcb12's CR2 on nested #VMEXIT to fix a
   bug where L2's CR2 can get corrupted after a save/restore, e.g. if the VM
   is migrated while L2 is faulting in memory.

 - Fix a class of nSVM bugs where some fields written by the CPU are not
   synchronized from vmcb02 to cached vmcb12 after VMRUN, and so are not
   up-to-date when saved by KVM_GET_NESTED_STATE.

 - Fix a class of bugs where the ordering between KVM_SET_NESTED_STATE and
   KVM_SET_{S}REGS could cause vmcb02 to be incorrectly initialized after
   save+restore.

 - Add a variety of missing nSVM consistency checks.

 - Fix several bugs where KVM failed to correctly update VMCB fields on nested
   #VMEXIT.

 - Fix several bugs where KVM failed to correctly synthesize #UD or #GP for
   SVM-related instructions.

 - Add support for save+restore of virtualized LBRs (on SVM).

 - Refactor various helpers and macros to improve clarity and (hopefully) make
   the code easier to maintain.

 - Aggressively sanitize fields when copying from vmcb12 to guard against
   unintentionally allowing L1 to utilize yet-to-be-defined features.

 - Fix several bugs where KVM botched rAX legality checks when emulating SVM
   instructions.  Note, KVM is still flawed in that KVM doesn't address size
   prefix overrides for 64-bit guests; this should probably be documented as a
   KVM erratum.

 - Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails instead of
   somewhat arbitrarily synthesizing #GP (i.e. don't bastardize AMD's already-
   sketchy behavior of generating #GP if for "unsupported" addresses).

 - Cache all used vmcb12 fields to further harden against TOCTOU bugs.
This commit is contained in:
Paolo Bonzini 2026-04-13 13:01:24 +02:00
commit ea8bc95fbb
24 changed files with 1230 additions and 490 deletions
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