Re: [PATCH v9 3/6] arm64: kvm: Save/restore MTE registers

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On 09/03/2021 17:27, Marc Zyngier wrote:

On Mon, 01 Mar 2021 14:23:12 +0000,
Steven Price <steven.price@xxxxxxx> wrote:


Define the new system registers that MTE introduces and context switch
them. The MTE feature is still hidden from the ID register as it isn't
supported in a VM yet.

Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
  arch/arm64/include/asm/kvm_host.h          |  6 ++
  arch/arm64/include/asm/kvm_mte.h           | 66 ++++++++++++++++++++++
  arch/arm64/include/asm/sysreg.h            |  3 +-
  arch/arm64/kernel/asm-offsets.c            |  3 +
  arch/arm64/kvm/hyp/entry.S                 |  7 +++
  arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 21 +++++++
  arch/arm64/kvm/sys_regs.c                  | 22 ++++++--
  7 files changed, 123 insertions(+), 5 deletions(-)
  create mode 100644 arch/arm64/include/asm/kvm_mte.h

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 1170ee137096..d00cc3590f6e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -208,6 +208,12 @@ enum vcpu_sysreg {
  	CNTP_CVAL_EL0,
  	CNTP_CTL_EL0,
+ /* Memory Tagging Extension registers */ 
+	RGSR_EL1,	/* Random Allocation Tag Seed Register */
+	GCR_EL1,	/* Tag Control Register */
+	TFSR_EL1,	/* Tag Fault Status Register (EL1) */
+	TFSRE0_EL1,	/* Tag Fault Status Register (EL0) */
+
  	/* 32bit specific registers. Keep them at the end of the range */
  	DACR32_EL2,	/* Domain Access Control Register */
  	IFSR32_EL2,	/* Instruction Fault Status Register */
diff --git a/arch/arm64/include/asm/kvm_mte.h b/arch/arm64/include/asm/kvm_mte.h
new file mode 100644
index 000000000000..6541c7d6ce06
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_mte.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#ifndef __ASM_KVM_MTE_H
+#define __ASM_KVM_MTE_H
+
+#ifdef __ASSEMBLY__
+
+#include <asm/sysreg.h>
+
+#ifdef CONFIG_ARM64_MTE
+
+.macro mte_switch_to_guest g_ctxt, h_ctxt, reg1
+alternative_if_not ARM64_MTE
+	b	.L__skip_switch\@
+alternative_else_nop_endif
+	mrs	\reg1, hcr_el2
+	and	\reg1, \reg1, #(HCR_ATA)
+	cbz	\reg1, .L__skip_switch\@
+
+	mrs_s	\reg1, SYS_RGSR_EL1
+	str	\reg1, [\h_ctxt, #CPU_RGSR_EL1]
+	mrs_s	\reg1, SYS_GCR_EL1
+	str	\reg1, [\h_ctxt, #CPU_GCR_EL1]
+
+	ldr	\reg1, [\g_ctxt, #CPU_RGSR_EL1]
+	msr_s	SYS_RGSR_EL1, \reg1
+	ldr	\reg1, [\g_ctxt, #CPU_GCR_EL1]
+	msr_s	SYS_GCR_EL1, \reg1
+
+.L__skip_switch\@:
+.endm
+
+.macro mte_switch_to_hyp g_ctxt, h_ctxt, reg1
+alternative_if_not ARM64_MTE
+	b	.L__skip_switch\@
+alternative_else_nop_endif
+	mrs	\reg1, hcr_el2
+	and	\reg1, \reg1, #(HCR_ATA)
+	cbz	\reg1, .L__skip_switch\@
+
+	mrs_s	\reg1, SYS_RGSR_EL1
+	str	\reg1, [\g_ctxt, #CPU_RGSR_EL1]
+	mrs_s	\reg1, SYS_GCR_EL1
+	str	\reg1, [\g_ctxt, #CPU_GCR_EL1]
+
+	ldr	\reg1, [\h_ctxt, #CPU_RGSR_EL1]
+	msr_s	SYS_RGSR_EL1, \reg1
+	ldr	\reg1, [\h_ctxt, #CPU_GCR_EL1]
+	msr_s	SYS_GCR_EL1, \reg1
+
+.L__skip_switch\@:
+.endm
+
+#else /* CONFIG_ARM64_MTE */
+
+.macro mte_switch_to_guest g_ctxt, h_ctxt, reg1
+.endm
+
+.macro mte_switch_to_hyp g_ctxt, h_ctxt, reg1
+.endm
+
+#endif /* CONFIG_ARM64_MTE */
+#endif /* __ASSEMBLY__ */
+#endif /* __ASM_KVM_MTE_H */
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index dfd4edbfe360..5424d195cf96 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -580,7 +580,8 @@
  #define SCTLR_ELx_M	(BIT(0))
#define SCTLR_ELx_FLAGS (SCTLR_ELx_M | SCTLR_ELx_A | SCTLR_ELx_C | \ 
-			 SCTLR_ELx_SA | SCTLR_ELx_I | SCTLR_ELx_IESB)
+			 SCTLR_ELx_SA | SCTLR_ELx_I | SCTLR_ELx_IESB | \
+			 SCTLR_ELx_ITFSB)
/* SCTLR_EL2 specific flags. */ 
  #define SCTLR_EL2_RES1	((BIT(4))  | (BIT(5))  | (BIT(11)) | (BIT(16)) | \
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index a36e2fc330d4..944e4f1f45d9 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -108,6 +108,9 @@ int main(void)
    DEFINE(VCPU_WORKAROUND_FLAGS,	offsetof(struct kvm_vcpu, arch.workaround_flags));
    DEFINE(VCPU_HCR_EL2,		offsetof(struct kvm_vcpu, arch.hcr_el2));
    DEFINE(CPU_USER_PT_REGS,	offsetof(struct kvm_cpu_context, regs));
+  DEFINE(CPU_RGSR_EL1,		offsetof(struct kvm_cpu_context, sys_regs[RGSR_EL1]));
+  DEFINE(CPU_GCR_EL1,		offsetof(struct kvm_cpu_context, sys_regs[GCR_EL1]));
+  DEFINE(CPU_TFSRE0_EL1,	offsetof(struct kvm_cpu_context, sys_regs[TFSRE0_EL1]));
    DEFINE(CPU_APIAKEYLO_EL1,	offsetof(struct kvm_cpu_context, sys_regs[APIAKEYLO_EL1]));
    DEFINE(CPU_APIBKEYLO_EL1,	offsetof(struct kvm_cpu_context, sys_regs[APIBKEYLO_EL1]));
    DEFINE(CPU_APDAKEYLO_EL1,	offsetof(struct kvm_cpu_context, sys_regs[APDAKEYLO_EL1]));
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index b0afad7a99c6..c67582c6dd55 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -13,6 +13,7 @@
  #include <asm/kvm_arm.h>
  #include <asm/kvm_asm.h>
  #include <asm/kvm_mmu.h>
+#include <asm/kvm_mte.h>
  #include <asm/kvm_ptrauth.h>
.text 
@@ -51,6 +52,9 @@ alternative_else_nop_endif
add x29, x0, #VCPU_CONTEXT + // mte_switch_to_guest(g_ctxt, h_ctxt, tmp1) 
+	mte_switch_to_guest x29, x1, x2
+
  	// Macro ptrauth_switch_to_guest format:
  	// 	ptrauth_switch_to_guest(guest cxt, tmp1, tmp2, tmp3)
  	// The below macro to restore guest keys is not implemented in C code
@@ -140,6 +144,9 @@ SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL)
  	// when this feature is enabled for kernel code.
  	ptrauth_switch_to_hyp x1, x2, x3, x4, x5
+ // mte_switch_to_hyp(g_ctxt, h_ctxt, reg1) 
+	mte_switch_to_hyp x1, x2, x3
+
  	// Restore hyp's sp_el0
  	restore_sp_el0 x2, x3
diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h 
index cce43bfe158f..de7e14c862e6 100644
--- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
+++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
@@ -14,6 +14,7 @@
  #include <asm/kvm_asm.h>
  #include <asm/kvm_emulate.h>
  #include <asm/kvm_hyp.h>
+#include <asm/kvm_mmu.h>
static inline void __sysreg_save_common_state(struct kvm_cpu_context *ctxt) 
  {
@@ -26,6 +27,16 @@ static inline void __sysreg_save_user_state(struct kvm_cpu_context *ctxt)
  	ctxt_sys_reg(ctxt, TPIDRRO_EL0)	= read_sysreg(tpidrro_el0);
  }
+static inline bool ctxt_has_mte(struct kvm_cpu_context *ctxt) 
+{
+	struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu;
+
+	if (!vcpu)
+		vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);
+
+	return kvm_has_mte(kern_hyp_va(vcpu->kvm));
+}
+
  static inline void __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
  {
  	ctxt_sys_reg(ctxt, CSSELR_EL1)	= read_sysreg(csselr_el1);
@@ -46,6 +57,11 @@ static inline void __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
  	ctxt_sys_reg(ctxt, PAR_EL1)	= read_sysreg_par();
  	ctxt_sys_reg(ctxt, TPIDR_EL1)	= read_sysreg(tpidr_el1);
+ if (ctxt_has_mte(ctxt)) { 
+		ctxt_sys_reg(ctxt, TFSR_EL1) = read_sysreg_el1(SYS_TFSR);
+		ctxt_sys_reg(ctxt, TFSRE0_EL1) = read_sysreg_s(SYS_TFSRE0_EL1);
+	}


Could TFSRE0_EL1 be synchronised on vcpu_load()/vcpu_put() instead of
being done eagerly on each save/restore? Same thing for TFSR_EL1 when
running VHE?
For TFSR_EL1 + VHE I believe it is synchronised only on vcpu_load/put - __sysreg_save_el1_state() is called from kvm_vcpu_load_sysregs_vhe().
TFSRE0_EL1 potentially could be improved. I have to admit I was unsure if it should be in __sysreg_save_user_state() instead. However AFAICT that is called at the same time as __sysreg_save_el1_state() and there's no optimisation for nVHE. And given it's an _EL1 register this seemed like the logic place.
Am I missing something here? Potentially there are other registers to be optimised (TPIDRRO_EL0 looks like a possiblity), but IMHO that doesn't belong in this series. 

> I'd like to keep the switch as lean as possible. I'm pretty sure this
> would simplify some of the "container_of()" ugliness above.
Yeah the container_of() isn't pretty - the alternative would be to stop treating __hyp_running_vcpu as a flag (instead add a real boolean for if the context is host/guest) and have it always point to the VCPU. I'm happy to make the change if you'd prefer it, but the downside is bloating the context unnecessarily. 

Thanks,

Steve


+
  	ctxt_sys_reg(ctxt, SP_EL1)	= read_sysreg(sp_el1);
  	ctxt_sys_reg(ctxt, ELR_EL1)	= read_sysreg_el1(SYS_ELR);
  	ctxt_sys_reg(ctxt, SPSR_EL1)	= read_sysreg_el1(SYS_SPSR);
@@ -107,6 +123,11 @@ static inline void __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
  	write_sysreg(ctxt_sys_reg(ctxt, PAR_EL1),	par_el1);
  	write_sysreg(ctxt_sys_reg(ctxt, TPIDR_EL1),	tpidr_el1);
+ if (ctxt_has_mte(ctxt)) { 
+		write_sysreg_el1(ctxt_sys_reg(ctxt, TFSR_EL1), SYS_TFSR);
+		write_sysreg_s(ctxt_sys_reg(ctxt, TFSRE0_EL1), SYS_TFSRE0_EL1);
+	}
+
  	if (!has_vhe() &&
  	    cpus_have_final_cap(ARM64_WORKAROUND_SPECULATIVE_AT) &&
  	    ctxt->__hyp_running_vcpu) {
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index e09dbc00b0a2..17cb6256f205 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1301,6 +1301,20 @@ static bool access_ccsidr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
  	return true;
  }
+static unsigned int mte_visibility(const struct kvm_vcpu *vcpu, 
+				   const struct sys_reg_desc *rd)
+{
+	return REG_HIDDEN;
+}
+
+#define MTE_REG(name) {				\
+	SYS_DESC(SYS_##name),			\
+	.access = undef_access,			\
+	.reset = reset_unknown,			\
+	.reg = name,				\
+	.visibility = mte_visibility,		\
+}
+
  /* sys_reg_desc initialiser for known cpufeature ID registers */
  #define ID_SANITISED(name) {			\
  	SYS_DESC(SYS_##name),			\
@@ -1469,8 +1483,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
  	{ SYS_DESC(SYS_ACTLR_EL1), access_actlr, reset_actlr, ACTLR_EL1 },
  	{ SYS_DESC(SYS_CPACR_EL1), NULL, reset_val, CPACR_EL1, 0 },
- { SYS_DESC(SYS_RGSR_EL1), undef_access }, 
-	{ SYS_DESC(SYS_GCR_EL1), undef_access },
+	MTE_REG(RGSR_EL1),
+	MTE_REG(GCR_EL1),
{ SYS_DESC(SYS_ZCR_EL1), NULL, reset_val, ZCR_EL1, 0, .visibility = sve_visibility }, 
  	{ SYS_DESC(SYS_TTBR0_EL1), access_vm_reg, reset_unknown, TTBR0_EL1 },
@@ -1496,8 +1510,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
  	{ SYS_DESC(SYS_ERXMISC0_EL1), trap_raz_wi },
  	{ SYS_DESC(SYS_ERXMISC1_EL1), trap_raz_wi },
- { SYS_DESC(SYS_TFSR_EL1), undef_access }, 
-	{ SYS_DESC(SYS_TFSRE0_EL1), undef_access },
+	MTE_REG(TFSR_EL1),
+	MTE_REG(TFSRE0_EL1),
{ SYS_DESC(SYS_FAR_EL1), access_vm_reg, reset_unknown, FAR_EL1 }, 
  	{ SYS_DESC(SYS_PAR_EL1), NULL, reset_unknown, PAR_EL1 },


Thanks,

	M.



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