diff options
| author | Fuad Tabba <tabba@google.com> | 2026-05-01 12:21:44 +0100 |
|---|---|---|
| committer | Marc Zyngier <maz@kernel.org> | 2026-05-07 14:12:41 +0100 |
| commit | d7396a72eae795d7f968fb451237b6ac1616d712 (patch) | |
| tree | 0b91ec3c528d1506017030e15de694949c5b029c | |
| parent | 54ea22273eef67196f238263bc79f27da04d2114 (diff) | |
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 <yaoyuan@linux.alibaba.com>
Assisted-by: Gemini:gemini-3.1-pro review-prompts
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260501112149.2824881-2-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
| -rw-r--r-- | arch/arm64/include/asm/sysreg.h | 2 |
1 files changed, 1 insertions, 1 deletions
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) |