On Wed, Mar 23, 2022 at 01:13:32PM -0700, Ricardo Koller wrote: > On Wed, Mar 23, 2022 at 07:53:14PM +0000, Oliver Upton wrote: > > Hi Reiji, > > > > On Thu, Mar 10, 2022 at 08:47:57PM -0800, Reiji Watanabe wrote: > > > Add hidden or reserved ID registers, and remaining ID registers, > > > which don't require special handling, to id_reg_desc_table. > > > Add 'flags' field to id_reg_desc, which is used to indicates hiddden > > > or reserved registers. Since now id_reg_desc_init() is called even > > > for hidden/reserved registers, change it to not do anything for them. > > > > > > Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx> > > > > I think there is a very important detail of the series that probably > > should be highlighted. We are only allowing AArch64 feature registers to > > be configurable, right? AArch32 feature registers remain visible with > > their default values passed through to the guest. If you've already > > stated this as a precondition elsewhere then my apologies for the noise. > > Aren't AArch64 ID regs architecturally mapped to their AArch32 > counterparts? They should show the same values. I'm not sure if it's a > problem (and if KVM is faithful to that rule), I believe it's a bit more subtle than that. The AArch32 feature registers are architecturally mapped to certain encodings accessible from AArch64. For example, ID_PFR0_EL1 is actually a 64 bit register where bits [31:0] map to the ID_PFR0 AArch32 register. ID_PFR0_EL1 is only accessible from AArch64 with the MRS instruction, and ID_PFR0 is only accessible from AArch32 with the MRC instruction. KVM just so happens to handle both of these reads from the same sys_reg_desc. AFAIK, there does not exist a direct bit mapping between the ID_*_EL1 <-> ID_AA64*_EL1 registers. But hey, could be wrong :) -- Thanks, Oliver
