From: Fuad Tabba Date: Fri, 1 May 2026 11:21:44 +0000 (+0100) Subject: KVM: arm64: Make EL2 exception entry and exit context-synchronization events X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d7396a72eae795d7f968fb451237b6ac1616d712;p=thirdparty%2Fkernel%2Fstable.git KVM: arm64: Make EL2 exception entry and exit context-synchronization events SCTLR_EL2.EIS and SCTLR_EL2.EOS control whether exception entry and exit at EL2 are Context Synchronisation Events (CSEs). Per ARM DDI 0487 M.b D24.2.175 (p. D24-9754): - !FEAT_ExS: the bit is RES1, so the entry/exit is unconditionally a CSE. - FEAT_ExS: the reset value is architecturally UNKNOWN; software must set the bit to make the entry/exit a CSE. INIT_SCTLR_EL2_MMU_ON in arch/arm64/include/asm/sysreg.h sets neither bit. KVM/arm64 hot paths rely on ERET from EL2 being a CSE, and on synchronous EL1->EL2 entry being a CSE, to elide explicit ISBs after MSRs to context-switching system registers (HCR_EL2, ZCR_EL2, ptrauth keys, etc.). On FEAT_ExS hardware those reliances are not architecturally backed unless EOS=1 (and, for entry, EIS=1). Until commit 0a35bd285f43 ("arm64: Convert SCTLR_EL2 to sysreg infrastructure"), SCTLR_EL2_RES1 was a hand-rolled mask that included BIT(11) (EOS) and BIT(22) (EIS), so INIT_SCTLR_EL2_MMU_ON was setting both unconditionally. The conversion made SCTLR_EL2_RES1 auto-generated; because the sysreg tooling only models unconditionally-RES1 fields and EIS/EOS are RES1 only when FEAT_ExS is absent, the auto-generated mask is UL(0). The seven other bits dropped from the old mask (positions 4, 5, 16, 18, 23, 28, 29) are unconditionally RES1 in the E2H=0 SCTLR_EL2 layout per DDI 0487 M.b D24.2.175, so dropping them is harmless. EIS and EOS are the only bits whose semantics changed for FEAT_ExS hardware and where the kernel relies on the value being 1. Make the guarantee explicit: include SCTLR_ELx_EIS | SCTLR_ELx_EOS in INIT_SCTLR_EL2_MMU_ON so that EL2 exception entry and exit are unconditionally CSEs regardless of whether FEAT_ExS is implemented. This matches the pairing in arch/arm64/kvm/config.c which treats EIS and EOS together as RES1 under !FEAT_ExS. Fixes: 0a35bd285f43 ("arm64: Convert SCTLR_EL2 to sysreg infrastructure") Reviewed-by: Yuan Yao Assisted-by: Gemini:gemini-3.1-pro review-prompts Signed-off-by: Fuad Tabba Link: https://patch.msgid.link/20260501112149.2824881-2-tabba@google.com Signed-off-by: Marc Zyngier --- diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index 736561480f36..7aa08d59d494 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -844,7 +844,7 @@ #define INIT_SCTLR_EL2_MMU_ON \ (SCTLR_ELx_M | SCTLR_ELx_C | SCTLR_ELx_SA | SCTLR_ELx_I | \ SCTLR_ELx_IESB | SCTLR_ELx_WXN | ENDIAN_SET_EL2 | \ - SCTLR_ELx_ITFSB | SCTLR_EL2_RES1) + SCTLR_ELx_ITFSB | SCTLR_ELx_EIS | SCTLR_ELx_EOS | SCTLR_EL2_RES1) #define INIT_SCTLR_EL2_MMU_OFF \ (SCTLR_EL2_RES1 | ENDIAN_SET_EL2)