Re: [PATCH v11 12/18] KVM: x86: Enable guest_memfd shared memory for SW-protected VMs

[David Hildenbrand <david@redhat.com>]

On 05.06.25 18:11, Fuad Tabba wrote:
> On Thu, 5 Jun 2025 at 16:49, David Hildenbrand <david@redhat.com> wrote:
>>
>> On 05.06.25 17:37, Fuad Tabba wrote:
>>> Define the architecture-specific macro to enable shared memory support
>>> in guest_memfd for relevant software-only VM types, specifically
>>> KVM_X86_DEFAULT_VM and KVM_X86_SW_PROTECTED_VM.
>>>
>>> Enable the KVM_GMEM_SHARED_MEM Kconfig option if KVM_SW_PROTECTED_VM is
>>> enabled.
>>>
>>> Co-developed-by: Ackerley Tng <ackerleytng@google.com>
>>> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
>>> Signed-off-by: Fuad Tabba <tabba@google.com>
>>> ---
>>>    arch/x86/include/asm/kvm_host.h | 10 ++++++++++
>>>    arch/x86/kvm/Kconfig            |  1 +
>>>    arch/x86/kvm/x86.c              |  3 ++-
>>>    3 files changed, 13 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>> index 709cc2a7ba66..ce9ad4cd93c5 100644
>>> --- a/arch/x86/include/asm/kvm_host.h
>>> +++ b/arch/x86/include/asm/kvm_host.h
>>> @@ -2255,8 +2255,18 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level,
>>>
>>>    #ifdef CONFIG_KVM_GMEM
>>>    #define kvm_arch_supports_gmem(kvm) ((kvm)->arch.supports_gmem)
>>> +
>>> +/*
>>> + * CoCo VMs with hardware support that use guest_memfd only for backing private
>>> + * memory, e.g., TDX, cannot use guest_memfd with userspace mapping enabled.
>>> + */
>>> +#define kvm_arch_supports_gmem_shared_mem(kvm)                       \
>>> +     (IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM) &&                      \
>>> +      ((kvm)->arch.vm_type == KVM_X86_SW_PROTECTED_VM ||             \
>>> +       (kvm)->arch.vm_type == KVM_X86_DEFAULT_VM))
>>>    #else
>>>    #define kvm_arch_supports_gmem(kvm) false
>>> +#define kvm_arch_supports_gmem_shared_mem(kvm) false
>>>    #endif
>>>
>>>    #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state)
>>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>>> index b37258253543..fdf24b50af9d 100644
>>> --- a/arch/x86/kvm/Kconfig
>>> +++ b/arch/x86/kvm/Kconfig
>>> @@ -47,6 +47,7 @@ config KVM_X86
>>>        select KVM_GENERIC_HARDWARE_ENABLING
>>>        select KVM_GENERIC_PRE_FAULT_MEMORY
>>>        select KVM_GENERIC_GMEM_POPULATE if KVM_SW_PROTECTED_VM
>>> +     select KVM_GMEM_SHARED_MEM if KVM_SW_PROTECTED_VM
>>>        select KVM_WERROR if WERROR
>>
>> Is $subject and this still true, given that it's now also supported for
>> KVM_X86_DEFAULT_VM?
> 
> True, just not the whole truth :)
> 
> I guess a better one would be, for Software VMs (remove protected)?

Now I am curious, what is a Hardware VM? :)

-- 
Cheers,

David / dhildenb