Re: [PATCH v10 02/28] KVM: VMX: Initialize VM entry/exit FRED controls in vmcs_config

[Sohil Mehta]

On 10/22/2026 8:10 PM, Sohil Mehta wrote:

> I couldn't find any precedent for this. I don't have a strong preference
> here. Is it worth making future-proof?


I did a bit of digging. The current entry in the table is the result of
Sean's preference provided early on in the FRED series. See

https://lore.kernel.org/all/Z739wdGmk4ZuWJ8v@xxxxxxxxxx/
https://lore.kernel.org/all/ZUz3cPmnqSq7Lol9@xxxxxxxxxx/

IIUC, we want the FRED entry/exit controls to be consistent without
depending on the ordering.

The current vmx_check_entry_exit_pairs() doesn't cover the FRED case (a
single entry bit mapping to two exit bits). So, the updated check would
cover this scenario.

> if (!(entry_controls & n_ctrl) == !(exit_controls & x_ctrl) &&
>     !(entry_controls & n_ctrl) == ((exit_controls & x_ctrl) != x_ctrl))
> 		continue;
> 


1st line: the entry control is set if and only if *any* exit bit is set.
2nd line: the entry control is set if and only if *all* exit bits are
set (which is specific to FRED for now).

Also, to make it easier to read, planning to reformat it as:

struct {
	u32 entry_control;
	u64 exit_control;
} const vmcs_entry_exit2_pairs[] = {
	{ VM_ENTRY_LOAD_IA32_FRED, SECONDARY_VM_EXIT_SAVE_IA32_FRED |
				   SECONDARY_VM_EXIT_LOAD_IA32_FRED },
};

Please let me know if you disagree with the approach.