From: Jon Doron arilou@gmail.com
[ Upstream commit f7d31e65368aeef973fab788aa22c4f1d5a6af66 ]
The problem the patch is trying to address is the fact that 'struct kvm_hyperv_exit' has different layout on when compiling in 32 and 64 bit modes.
In 64-bit mode the default alignment boundary is 64 bits thus forcing extra gaps after 'type' and 'msr' but in 32-bit mode the boundary is at 32 bits thus no extra gaps.
This is an issue as even when the kernel is 64 bit, the userspace using the interface can be both 32 and 64 bit but the same 32 bit userspace has to work with 32 bit kernel.
The issue is fixed by forcing the 64 bit layout, this leads to ABI change for 32 bit builds and while we are obviously breaking '32 bit userspace with 32 bit kernel' case, we're fixing the '32 bit userspace with 64 bit kernel' one.
As the interface has no (known) users and 32 bit KVM is rather baroque nowadays, this seems like a reasonable decision.
Reviewed-by: Vitaly Kuznetsov vkuznets@redhat.com Signed-off-by: Jon Doron arilou@gmail.com Message-Id: 20200424113746.3473563-2-arilou@gmail.com Reviewed-by: Roman Kagan rvkagan@yandex-team.ru Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/virtual/kvm/api.txt | 2 ++ include/uapi/linux/kvm.h | 2 ++ 2 files changed, 4 insertions(+)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index f67ed33d1054..81a8802cea88 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -3737,9 +3737,11 @@ EOI was received. #define KVM_EXIT_HYPERV_SYNIC 1 #define KVM_EXIT_HYPERV_HCALL 2 __u32 type; + __u32 pad1; union { struct { __u32 msr; + __u32 pad2; __u64 control; __u64 evt_page; __u64 msg_page; diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 27c62abb6c9e..efe8873943f6 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -189,9 +189,11 @@ struct kvm_hyperv_exit { #define KVM_EXIT_HYPERV_SYNIC 1 #define KVM_EXIT_HYPERV_HCALL 2 __u32 type; + __u32 pad1; union { struct { __u32 msr; + __u32 pad2; __u64 control; __u64 evt_page; __u64 msg_page;