[PATCH] KVM: arm64: Set HCR_EL2.BSU to Inner Shareable for guests

[PATCH] KVM: arm64: Set HCR_EL2.BSU to Inner Shareable for guests

[Fuad Tabba]

KVM sets HCR_EL2.BSU to Inner Shareable for guests, so that a guest's
barriers cover the TLB and I-cache invalidations that HCR_EL2.FB
broadcasts. However, since HCR_BSU_IS became an alias of the generated
HCR_EL2_BSU_IS, it is the unshifted field value 0b01, which sets bit
0 (VM, already set) and leaves BSU at 0b00. A guest's DSB NSH is then
not required to wait for a broadcast TLBI to complete on other CPUs.

Build the field with SYS_FIELD_PREP_ENUM().

Fixes: d0f39259eff4 ("arm64: sysreg: Add layout for HCR_EL2")
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
Found while testing Marc's HCR cleanup [1]. Its patch 1 carries this
line over as HCR_EL2_BSU_IS, so on top of this fix that hunk would
keep SYS_FIELD_PREP_ENUM() instead. I can also rebase this on top of
the series if that's easier.

[1] https://lore.kernel.org/r/20261015173605.1072963-1-maz@kernel.org

 arch/arm64/include/asm/kvm_arm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 4bfbd827c5aa7..b3e9dd302730e 100644
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -98,7 +98,7 @@
  * TID1:	Trap REVIDR_EL1, AIDR_EL1, and SMIDR_EL1
  */
 #define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \
-			 HCR_BSU_IS | HCR_FB | HCR_TACR | \
+			 SYS_FIELD_PREP_ENUM(HCR_EL2, BSU, IS) | HCR_EL2_FB | HCR_EL2_TACR | \
 			 HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \
 			 HCR_FMO | HCR_IMO | HCR_PTW | HCR_TID3 | HCR_TID1)
 #define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK)
-- 
2.39.5