On 7/15/21 1:39 PM, Sean Christopherson wrote:
On Thu, Jul 15, 2021, Brijesh Singh wrote:
The memfd_secrets uses the set_direct_map_{invalid,default}_noflush() and it
is designed to remove/add the present bit in the direct map. We can't use
them, because in our case the page may get accessed by the KVM (e.g
kvm_guest_write, kvm_guest_map etc).
But KVM should never access a guest private page, i.e. the direct map should
always be restored to PRESENT before KVM attempts to access the page.
Yes, KVM should *never* access the guest private pages. So, we could
potentially enhance the RMPUPDATE() to check for the assigned and act
accordingly.
Are you thinking something along the line of this:
int rmpupdate(struct page *page, struct rmpupdate *val)
{
...
/*
* If page is getting assigned in the RMP entry then unmap
* it from the direct map before its added in the RMP table.
*/
if (val.assigned)
set_direct_map_invalid_noflush(page_to_virt(page), 1);
...
/*
* If the page is getting unassigned then restore the mapping
* in the direct map after its removed from the RMP table.
*/
if (!val.assigned)
set_direct_map_default_noflush(page_to_virt(page), 1);
...
}
thanks
