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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Sep 2025 11:06:31.0303 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 882dd958-5d74-406b-8999-08ddea10c58f X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB3PEPF00008860.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU2PR08MB7326 Hi Dave, [...] > > > > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S > > > > index 36e2d26b54f5..ac12f1b4f8e2 100644 > > > > --- a/arch/arm64/kernel/hyp-stub.S > > > > +++ b/arch/arm64/kernel/hyp-stub.S > > > > @@ -144,7 +144,17 @@ SYM_CODE_START_LOCAL(__finalise_el2) > > > > > > > > .Lskip_indirection: > > > > .Lskip_tcr2: > > > > + mrs_s x1, SYS_ID_AA64MMFR3_EL1 > > > > + ubfx x1, x1, #ID_AA64MMFR3_EL1_SCTLRX_SHIFT, #4 > > > > + cbz x1, .Lskip_sctlr2 > > > > + mrs_s x1, SYS_SCTLR2_EL12 > > > > + msr_s SYS_SCTLR2_EL1, x1 > > > > > > > > + // clean SCTLR2_EL1 > > > > + mov_q x1, INIT_SCTLR2_EL1 > > > > + msr_s SYS_SCTLR2_EL12, x1 > > > > > > I'm still not sure why we need to do this. The code doesn't seem to > > > clean up by the EL1 value of any other register -- or have I missed > > > something? > > > > > > We have already switched to EL2, via the HVC call that jumped to > > > __finalise_el2. We won't run at EL1 again unless KVM starts a guest -- > > > but in that case, it's KVM's responsibility to set up the EL1 registers > > > before handing control to the guest. > > > > > > In any case, is SCTLR2_EL1 ever set to anything except INIT_SCTLR2_EL1 > > > before we get here? > > > > Regardless of VHE and nVHE, between init_kernel_el() and finalise_el2() > > the kernel modifies SCTLR_EL1/SCTLR2_EL1 (since el level in this period > > is EL1). > > and at the end of finalise_el2(), kernel switches to el2 and > > if VHE, it writes the SCTLR_EL1/SCTLR2_EL1 to SCTLR_EL2/SCTLR2_EL2 and > > initialize the SCTLR_EL1/SCTLR2_EL1. > > > > Although there is no code to modify SCTLR2_EL1 between this period, > > as SCTLR1_ELx, I initialize the SCTLR2_EL1 as init value for the future > > usage. > > I think that we don't need to ensure that all sysregs are cleanly > initialised; only those that can affect execution in some way need to > be initialised. > > Once we are running at EL2 with VHE, we don't switch back to EL1, so > the _EL1 control registers don't affect execution any more. > > If we did have to clean up the _EL1 registers, then this code would > need to clean up all the other regs too, but I can't see clean-up for > anything other than SCTLR2_EL1 here. Is there some cleanup code > elsewhere that I have missed? > > Cheers > ---Dave When I look at init_el2(), it returns to EL1 via: mov x0, #INIT_PSTATE_EL1 msr spsr_el2, x0 ... eret In other words, from init_kernel_el() through finalise_el2(), all system-register accesses are made at EL1 (i.e., SYS_REG_EL1). During this period, it appears that only SCTLR_EL1 is modified, so the code only needs to care about the accessed register — SCTLR_EL1. That’s why SCTLR_EL1 is reinitialised at the end of finalise_el2(). Otherwise, the MMU bit might remain enabled, which could cause errors later when launching a VM under VHE. However, the idea behind this patch is to initialise SCTLR2_ELx the same way as SCTLR_ELx. I’m not sure whether SCTLR2_ELx is modified during this period. If it is (now or in the future), it should be cleared/reinitialised just like SCTLR_EL1. This patch is based on the assumption that there may be modifications to SCTLR2_ELx during this period. So it isn’t about other system registers; it’s about the register actually used during this period. Am I missing anything? Thanks! -- Sincerely, Yeoreum Yun