Re: [PATCH v14 4/5] KVM: arm64: Set PSTATE.EXLOCK when entering an exception

On Sat, Oct 05, 2024 at 01:36:09PM +0100, Marc Zyngier wrote:

Mark Brown broonie@kernel.org wrote:

...

• // PSTATE.EXLOCK is set to 0 upon any exception to a higher
• // EL, or to GCSCR_ELx.EXLOCKEN for an exception to the same
• // exception level. See ARM DDI 0487 RWTXBY, D.1.3.2 in K.a.
• if (kvm_has_gcs(vcpu->kvm) &&

•    (target_mode & PSR_EL_MASK) == (mode & PSR_EL_MASK)) {
  

• u64 gcscr = __vcpu_read_sys_reg(vcpu, GCSCR_EL1);
  

No, please. This only works by luck when a guest has AArch32 EL0, and creates more havoc on a NV guest. In general, this PSR_EL_MASK creates more problem than anything else, and doesn't fit the rest of the code.

You say luck, I say careful architecture definition but sure.

So this needs to:

• explicitly only apply to exceptions from AArch64
• handle exception from EL2, since this helper already deals with that

The latter point of course means introducing GCSCR_EL2 (and everything that depends on it, such as the trap handling).

For clarity, which trap handling specifically?