[PATCH v5 5/7] KVM: selftests: Make arm64's MMIO ucall multi-VM friendly

[Andrew Jones]

On Thu, Aug 25, 2022 at 11:25:20PM +0000, Sean Christopherson wrote:
> Fix a mostly-theoretical bug where ARM's ucall MMIO setup could result in
> different VMs stomping on each other by cloberring the global pointer.
> 
> Fix the most obvious issue by saving the MMIO gpa into the VM.
> 
> A more subtle bug is that creating VMs in parallel (on multiple tasks)
> could result in a VM using the wrong address.  Synchronizing a global to
> a guest effectively snapshots the value on a per-VM basis, i.e. the
> "global" is already prepped to work with multiple VMs, but setting the
> global in the host is not thread-safe.  To fix that bug, add
> write_guest_global() to allow stuffing a VM's copy of a "global" without
> modifying the host value.
> 
> Signed-off-by: Sean Christopherson <seanjc at google.com>
> ---
>  .../selftests/kvm/include/kvm_util_base.h     | 15 +++++++++++++++
>  .../testing/selftests/kvm/lib/aarch64/ucall.c | 19 ++++++++++++++-----
>  2 files changed, 29 insertions(+), 5 deletions(-)
>

Reviewed-by: Andrew Jones <andrew.jones at linux.dev>