Re: [PATCH v2 11/14] powerpc/64s: Clear/restore caller gprs in syscall interrupt/return

On 11 Aug 2022, at 8:11 pm, Andrew Donnellan [off-list ref] wrote:

On Mon, 2022-07-25 at 16:31 +1000, Rohan McLure wrote:

quoted

Clear user state in gprs (assign to zero) to reduce the influence of
user
registers on speculation within kernel syscall handlers. Clears occur
at the very beginning of the sc and scv 0 interrupt handlers, with
restores occurring following the execution of the syscall handler.

One function of syscall_exit_prepare is to determine when non-
volatile
regs must be restored, and it still serves that purpose on 32-bit.
Use
it now for determining where to find XER, CTR, CR.

I'm not sure exactly how syscall_exit_prepare comes into this?

Apologies, this comment belongs in patch 14 and concerns interrupt_exit_user_prepare.