On 9/11/2021 7:55 AM, Sean Christopherson wrote:
On Fri, Sep 10, 2021, Sean Christopherson wrote:
On Mon, Aug 09, 2021, Zeng Guang wrote:
+ if (!pages)
+ return -ENOMEM;
+
+ to_kvm_vmx(kvm)->pid_table = (void *)page_address(pages);
+ to_kvm_vmx(kvm)->pid_last_index = KVM_MAX_VCPU_ID;
I don't see the point of pid_last_index if we're hardcoding it to KVM_MAX_VCPU_ID.
If I understand the ucode pseudocode, there's no performance hit in the happy
case, i.e. it only guards against out-of-bounds accesses.
And I wonder if we want to fail the build if this grows beyond an order-1
allocation, e.g.
BUILD_BUG_ON(PID_TABLE_ORDER > 1);
Allocating two pages per VM isn't terrible, but 4+ starts to get painful when
considering the fact that most VMs aren't going to need more than one page. For
now I agree the simplicity of not dynamically growing the table is worth burning
a page.
Ugh, Paolo has queued a series which bumps KVM_MAX_VCPU_ID to 4096[*]. That makes
this an order-3 allocation, which is quite painful. One thought would be to let
userspace declare the max vCPU it wants to create, not sure if that would work for
xAPIC though.
[*] https://lkml.kernel.org/r/1111efc8-b32f-bd50-2c0f-4c6f506b544b@xxxxxxxxxx
Thus we keep current design as no change.
