Re: [PATCH v1 10/24] kvm: arm64: Extract parts of el2_setup into a macro

From: Marc Zyngier
Date: Tue Nov 10 2020 - 10:56:09 EST

On 2020-11-09 11:32, David Brazdil wrote:
When the a CPU is booted in EL2, the kernel checks for VHE support and
initializes the CPU core accordingly. For nVHE it also installs the stub
vectors and drops down to EL1.

Once KVM gains the ability to boot cores without going through the
kernel entry point, it will need to initialize the CPU the same way.
Extract the relevant bits of el2_setup into init_el2_state macro
with an argument specifying whether to initialize for VHE or nVHE.

No functional change. Size of el2_setup increased by 148 bytes due
to duplication.

Signed-off-by: David Brazdil <dbrazdil@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_asm.h | 128 ++++++++++++++++++++++++++++
arch/arm64/kernel/head.S | 140 +++----------------------------
2 files changed, 141 insertions(+), 127 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index a49a87a186c3..893327d1e449 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -331,6 +331,134 @@ extern char
__smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ];
msr sp_el0, \tmp
.endm

+.macro init_el2_state mode
+
+.ifnes "\mode", "vhe"
+.ifnes "\mode", "nvhe"
+.error "Invalid 'mode' argument"
+.endif
+.endif
+
+ mov_q x0, (SCTLR_EL2_RES1 | ENDIAN_SET_EL2)
+ msr sctlr_el2, x0
+ isb
+
+ /*
+ * Allow Non-secure EL1 and EL0 to access physical timer and counter.
+ * This is not necessary for VHE, since the host kernel runs in EL2,
+ * and EL0 accesses are configured in the later stage of boot process.
+ * Note that when HCR_EL2.E2H == 1, CNTHCTL_EL2 has the same bit layout
+ * as CNTKCTL_EL1, and CNTKCTL_EL1 accessing instructions are redefined
+ * to access CNTHCTL_EL2. This allows the kernel designed to run at EL1
+ * to transparently mess with the EL0 bits via CNTKCTL_EL1 access in
+ * EL2.
+ */
+.ifeqs "\mode", "nvhe"
+ mrs x0, cnthctl_el2
+ orr x0, x0, #3 // Enable EL1 physical timers
+ msr cnthctl_el2, x0
+.endif
+ msr cntvoff_el2, xzr // Clear virtual offset
+
+#ifdef CONFIG_ARM_GIC_V3
+ /* GICv3 system register access */
+ mrs x0, id_aa64pfr0_el1
+ ubfx x0, x0, #ID_AA64PFR0_GIC_SHIFT, #4
+ cbz x0, 3f
+
+ mrs_s x0, SYS_ICC_SRE_EL2
+ orr x0, x0, #ICC_SRE_EL2_SRE // Set ICC_SRE_EL2.SRE==1
+ orr x0, x0, #ICC_SRE_EL2_ENABLE // Set ICC_SRE_EL2.Enable==1
+ msr_s SYS_ICC_SRE_EL2, x0
+ isb // Make sure SRE is now set
+ mrs_s x0, SYS_ICC_SRE_EL2 // Read SRE back,
+ tbz x0, #0, 3f // and check that it sticks
+ msr_s SYS_ICH_HCR_EL2, xzr // Reset ICC_HCR_EL2 to defaults
+3:
+#endif
+
+ /* Populate ID registers. */
+ mrs x0, midr_el1
+ mrs x1, mpidr_el1
+ msr vpidr_el2, x0
+ msr vmpidr_el2, x1

I don't think this has any effect on VHE, and could be lumped
together with the nVHE code.

+
+#ifdef CONFIG_COMPAT
+ msr hstr_el2, xzr // Disable CP15 traps to EL2
+#endif
+
+ /* EL2 debug */
+ mrs x1, id_aa64dfr0_el1
+ sbfx x0, x1, #ID_AA64DFR0_PMUVER_SHIFT, #4
+ cmp x0, #1
+ b.lt 4f // Skip if no PMU present
+ mrs x0, pmcr_el0 // Disable debug access traps
+ ubfx x0, x0, #11, #5 // to EL2 and allow access to
+4:
+ csel x3, xzr, x0, lt // all PMU counters from EL1
+
+ /* Statistical profiling */
+ ubfx x0, x1, #ID_AA64DFR0_PMSVER_SHIFT, #4
+ cbz x0, 7f // Skip if SPE not present
+.ifeqs "\mode", "nvhe"
+ mrs_s x4, SYS_PMBIDR_EL1 // If SPE available at EL2,
+ and x4, x4, #(1 << SYS_PMBIDR_EL1_P_SHIFT)
+ cbnz x4, 5f // then permit sampling of physical
+ mov x4, #(1 << SYS_PMSCR_EL2_PCT_SHIFT | \
+ 1 << SYS_PMSCR_EL2_PA_SHIFT)
+ msr_s SYS_PMSCR_EL2, x4 // addresses and physical counter
+5:
+ mov x1, #(MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT)
+ orr x3, x3, x1 // If we don't have VHE, then
+ b 7f // use EL1&0 translation.
+.endif
+ orr x3, x3, #MDCR_EL2_TPMS // and disable access from EL1

This orr would probably be better placed in an "else" close to the
previous macro. And since you are making things "modular", why not
go the extra mile, and define macros for each functionality that
defer between modes? It would certainly make this change more digest,
and the result more readable.

+7:
+ msr mdcr_el2, x3 // Configure debug traps
+
+ /* LORegions */
+ mrs x1, id_aa64mmfr1_el1
+ ubfx x0, x1, #ID_AA64MMFR1_LOR_SHIFT, 4
+ cbz x0, 1f
+ msr_s SYS_LORC_EL1, xzr
+1:
+
+ /* Stage-2 translation */
+ msr vttbr_el2, xzr
+
+.ifeqs "\mode", "nvhe"
+ /*
+ * When VHE is not in use, early init of EL2 and EL1 needs to be
+ * done here.
+ * When VHE _is_ in use, EL1 will not be used in the host and
+ * requires no configuration, and all non-hyp-specific EL2 setup
+ * will be done via the _EL1 system register aliases in __cpu_setup.
+ */
+ mov_q x0, (SCTLR_EL1_RES1 | ENDIAN_SET_EL1)
+ msr sctlr_el1, x0
+
+ /* Coprocessor traps. */
+ mov x0, #0x33ff
+ msr cptr_el2, x0 // Disable copro. traps to EL2
+
+ /* SVE register access */
+ mrs x1, id_aa64pfr0_el1
+ ubfx x1, x1, #ID_AA64PFR0_SVE_SHIFT, #4
+ cbz x1, 7f
+
+ bic x0, x0, #CPTR_EL2_TZ // Also disable SVE traps
+ msr cptr_el2, x0 // Disable copro. traps to EL2
+ isb
+ mov x1, #ZCR_ELx_LEN_MASK // SVE: Enable full vector
+ msr_s SYS_ZCR_EL2, x1 // length for EL1.
+
+ /* spsr */
+7: mov x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
+ PSR_MODE_EL1h)
+ msr spsr_el2, x0
+.endif
+.endm
+
#endif

#endif /* __ARM_KVM_ASM_H__ */
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index d8d9caf02834..e7270b63abed 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -25,6 +25,7 @@
#include <asm/image.h>
#include <asm/kernel-pgtable.h>
#include <asm/kvm_arm.h>
+#include <asm/kvm_asm.h>
#include <asm/memory.h>
#include <asm/pgtable-hwdef.h>
#include <asm/page.h>
@@ -499,153 +500,38 @@ SYM_FUNC_START(el2_setup)
isb
ret

-1: mov_q x0, (SCTLR_EL2_RES1 | ENDIAN_SET_EL2)
- msr sctlr_el2, x0
-
+1:
#ifdef CONFIG_ARM64_VHE
/*
- * Check for VHE being present. For the rest of the EL2 setup,
- * x2 being non-zero indicates that we do have VHE, and that the
- * kernel is intended to run at EL2.
+ * Check for VHE being present. x2 being non-zero indicates that we
+ * do have VHE, and that the kernel is intended to run at EL2.
*/
mrs x2, id_aa64mmfr1_el1
ubfx x2, x2, #ID_AA64MMFR1_VHE_SHIFT, #4
-#else
- mov x2, xzr
-#endif
+ cbz x2, el2_setup_nvhe

What initialises x2 to zero when CONFIG_VHE is disabled?

Thanks,

M.
--
Jazz is not dead. It just smells funny...