[v4,00/13] KVM: xen: update shared_info and vcpu_info handling

Message

Paul Durrant Sept. 19, 2023, 1:41 p.m. UTC

From: Paul Durrant <[e-mail]>

Changed in v4:
 - The offset into the cache returned from get_vcpu_info_cache() was not
   being factored into kvm_gpc_check() or kvm_gpc_refresh() calls. Fix
   this.
 - When transitioning from a default vcpu_info to an explicit one, copy
   the content across. This was previously the responsibility of the
   VMM.

Changed in v3:
 - Patch added to make sure Xen vcpu_id is immutable once shared_info is
   set.
 - Adjust the xen_shinfo_test selftest accordingly.
 - Also have the selftest use both mechanisms to set shared_info.
 - Add text to API documentation discussing copying of vcpu_info. This
   has been removed in v4.
 - Adjust the selftest to switch from default to explicit vcpu_info
   part way through.

Changed in v2:
 - Defer advertizement of KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA to a patch
   at the end of the series.
 - Remove the KVM_XEN_HVM_CONFIG_DEFAULT_VCPU_INFO capability.
 - Add selftests and API documentation.

Original text:

Currently we treat the shared_info page as guest memory and the VMM informs
KVM of its location using a GFN. However it is not guest memory as such;
it's an overlay page. So we pointlessly invalidate and re-cache a mapping
to the *same page* of memory every time the guest requests that shared_info
be mapped into its address space. Let's avoid doing that by modifying the
pfncache code to allow activation using a fixed userspace HVA as well as
a GPA.

Also, if the guest does not hypercall to explicitly set a pointer to a
vcpu_info in its own memory, the default vcpu_info embedded in the
shared_info page should be used. At the moment the VMM has to set up a
pointer to the structure explicitly (again treating it like it's in
guest memory, despite being in an overlay page). Let's also avoid the
need for that. We already have a cached mapping for the shared_info
page so just use that directly by default.

Paul Durrant (13):
  KVM: pfncache: add a map helper function
  KVM: pfncache: add a mark-dirty helper
  KVM: pfncache: add a helper to get the gpa
  KVM: pfncache: base offset check on khva rather than gpa
  KVM: pfncache: allow a cache to be activated with a fixed (userspace)
    HVA
  KVM: xen: allow shared_info to be mapped by fixed HVA
  KVM: xen: prepare for using 'default' vcpu_info
  KVM: xen: prevent vcpu_id from changing whilst shared_info is valid
  KVM: xen: automatically use the vcpu_info embedded in shared_info
  KVM: selftests / xen: set KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID
  KVM: selftests / xen: map shared_info using HVA rather than GFN
  KVM: selftests / xen: don't explicitly set the vcpu_info address
  KVM: xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability

 Documentation/virt/kvm/api.rst                |  52 ++--
 arch/x86/include/asm/kvm_host.h               |   4 +
 arch/x86/kvm/x86.c                            |  17 +-
 arch/x86/kvm/xen.c                            | 244 ++++++++++++++----
 arch/x86/kvm/xen.h                            |   6 +-
 include/linux/kvm_host.h                      |  43 +++
 include/linux/kvm_types.h                     |   3 +-
 include/uapi/linux/kvm.h                      |   6 +-
 .../selftests/kvm/x86_64/xen_shinfo_test.c    |  75 +++++-
 virt/kvm/pfncache.c                           | 129 ++++++---
 10 files changed, 454 insertions(+), 125 deletions(-)
---
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Paolo Bonzini <[e-mail]>
Cc: Sean Christopherson <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]