[RFC PATCH 0/3] KVM: x86: honor guest memory type

[Paolo Bonzini]

On 13/02/20 22:30, Chia-I Wu wrote:
> Hi,
> 
> Host GPU drivers like to give userspace WC mapping.  When the userspace makes
> the mapping available to a guest, it also tells the guest to create a WC
> mapping.  However, even when the guest kernel picks the correct memory type,
> it gets ignored because of VMX_EPT_IPAT_BIT on Intel.
> 
> This series adds a new flag to KVM_SET_USER_MEMORY_REGION, which tells the
> host kernel to honor the guest memory type for the memslot.  An alternative
> fix is for KVM to unconditionally honor the guest memory type (unless it is
> MMIO, to avoid MCEs on Intel).  I believe the alternative fix is how things
> are on ARM, and probably also how things are on AMD.
> 
> I am new to KVM and HW virtualization technologies.  This series is meant as
> an RFC.
> 

When we tried to do this in the past, we got machine checks everywhere
unfortunately due to the same address being mapped with different memory
types.  Unfortunately I cannot find the entry anymore in bugzilla, but
this was not fixed as far as I know.

Paolo