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linux/arch/arm64/kvm/hyp/exception.c
Marc Zyngier e3f6836a63 KVM: arm64: Simplify sysreg access on exception delivery 
Distinguishing between NV and VHE is slightly pointless, and only
serves as an extra complication, or a way to introduce bugs, such
as the way SPSR_EL1 gets written without checking for the state
being resident.

Get rid if this silly distinction, and fix the bug in one go.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250817121926.217900-3-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
2025-08-28 11:39:48 -07:00

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Fault injection for both 32 and 64bit guests.
*
* Copyright (C) 2012,2013 - ARM Ltd
* Author: Marc Zyngier <marc.zyngier@arm.com>
*
* Based on arch/arm/kvm/emulate.c
* Copyright (C) 2012 - Virtual Open Systems and Columbia University
* Author: Christoffer Dall <c.dall@virtualopensystems.com>
*/
#include <hyp/adjust_pc.h>
#include <linux/kvm_host.h>
#include <asm/kvm_emulate.h>
#include <asm/kvm_mmu.h>
#include <asm/kvm_nested.h>
#if !defined (__KVM_NVHE_HYPERVISOR__) && !defined (__KVM_VHE_HYPERVISOR__)
#error Hypervisor code only!
#endif
static inline u64 __vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
{
if (has_vhe())
return vcpu_read_sys_reg(vcpu, reg);
return __vcpu_sys_reg(vcpu, reg);
}
static inline void __vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg)
{
if (has_vhe())
vcpu_write_sys_reg(vcpu, val, reg);
else
__vcpu_assign_sys_reg(vcpu, reg, val);
}
static void __vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long target_mode,
u64 val)
{
if (has_vhe()) {
if (target_mode == PSR_MODE_EL1h)
vcpu_write_sys_reg(vcpu, val, SPSR_EL1);
else
vcpu_write_sys_reg(vcpu, val, SPSR_EL2);
} else {
__vcpu_assign_sys_reg(vcpu, SPSR_EL1, val);
}
}
static void __vcpu_write_spsr_abt(struct kvm_vcpu *vcpu, u64 val)
{
if (has_vhe() && vcpu_get_flag(vcpu, SYSREGS_ON_CPU))
write_sysreg(val, spsr_abt);
else
vcpu->arch.ctxt.spsr_abt = val;
}
static void __vcpu_write_spsr_und(struct kvm_vcpu *vcpu, u64 val)
{
if (has_vhe() && vcpu_get_flag(vcpu, SYSREGS_ON_CPU))
write_sysreg(val, spsr_und);
else
vcpu->arch.ctxt.spsr_und = val;
}
/*
* This performs the exception entry at a given EL (@target_mode), stashing PC
* and PSTATE into ELR and SPSR respectively, and compute the new PC/PSTATE.
* The EL passed to this function *must* be a non-secure, privileged mode with
* bit 0 being set (PSTATE.SP == 1).
*
* When an exception is taken, most PSTATE fields are left unchanged in the
* handler. However, some are explicitly overridden (e.g. M[4:0]). Luckily all
* of the inherited bits have the same position in the AArch64/AArch32 SPSR_ELx
* layouts, so we don't need to shuffle these for exceptions from AArch32 EL0.
*
* For the SPSR_ELx layout for AArch64, see ARM DDI 0487E.a page C5-429.
* For the SPSR_ELx layout for AArch32, see ARM DDI 0487E.a page C5-426.
*
* Here we manipulate the fields in order of the AArch64 SPSR_ELx layout, from
* MSB to LSB.
*/
static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode,
enum exception_type type)
{
unsigned long sctlr, vbar, old, new, mode;
u64 exc_offset;
mode = *vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT);
if (mode == target_mode)
exc_offset = CURRENT_EL_SP_ELx_VECTOR;
else if ((mode | PSR_MODE_THREAD_BIT) == target_mode)
exc_offset = CURRENT_EL_SP_EL0_VECTOR;
else if (!(mode & PSR_MODE32_BIT))
exc_offset = LOWER_EL_AArch64_VECTOR;
else
exc_offset = LOWER_EL_AArch32_VECTOR;
switch (target_mode) {
case PSR_MODE_EL1h:
vbar = __vcpu_read_sys_reg(vcpu, VBAR_EL1);
sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
__vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL1);
break;
case PSR_MODE_EL2h:
vbar = __vcpu_read_sys_reg(vcpu, VBAR_EL2);
sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL2);
__vcpu_write_sys_reg(vcpu, *vcpu_pc(vcpu), ELR_EL2);
break;
default:
/* Don't do that */
BUG();
}
*vcpu_pc(vcpu) = vbar + exc_offset + type;
old = *vcpu_cpsr(vcpu);
new = 0;
new |= (old & PSR_N_BIT);
new |= (old & PSR_Z_BIT);
new |= (old & PSR_C_BIT);
new |= (old & PSR_V_BIT);
if (kvm_has_mte(kern_hyp_va(vcpu->kvm)))
new |= PSR_TCO_BIT;
new |= (old & PSR_DIT_BIT);
// PSTATE.UAO is set to zero upon any exception to AArch64
// See ARM DDI 0487E.a, page D5-2579.
// PSTATE.PAN is unchanged unless SCTLR_ELx.SPAN == 0b0
// SCTLR_ELx.SPAN is RES1 when ARMv8.1-PAN is not implemented
// See ARM DDI 0487E.a, page D5-2578.
new |= (old & PSR_PAN_BIT);
if (!(sctlr & SCTLR_EL1_SPAN))
new |= PSR_PAN_BIT;
// PSTATE.SS is set to zero upon any exception to AArch64
// See ARM DDI 0487E.a, page D2-2452.
// PSTATE.IL is set to zero upon any exception to AArch64
// See ARM DDI 0487E.a, page D1-2306.
// PSTATE.SSBS is set to SCTLR_ELx.DSSBS upon any exception to AArch64
// See ARM DDI 0487E.a, page D13-3258
if (sctlr & SCTLR_ELx_DSSBS)
new |= PSR_SSBS_BIT;
// PSTATE.BTYPE is set to zero upon any exception to AArch64
// See ARM DDI 0487E.a, pages D1-2293 to D1-2294.
new |= PSR_D_BIT;
new |= PSR_A_BIT;
new |= PSR_I_BIT;
new |= PSR_F_BIT;
new |= target_mode;
*vcpu_cpsr(vcpu) = new;
__vcpu_write_spsr(vcpu, target_mode, old);
}
/*
* When an exception is taken, most CPSR fields are left unchanged in the
* handler. However, some are explicitly overridden (e.g. M[4:0]).
*
* The SPSR/SPSR_ELx layouts differ, and the below is intended to work with
* either format. Note: SPSR.J bit doesn't exist in SPSR_ELx, but this bit was
* obsoleted by the ARMv7 virtualization extensions and is RES0.
*
* For the SPSR layout seen from AArch32, see:
* - ARM DDI 0406C.d, page B1-1148
* - ARM DDI 0487E.a, page G8-6264
*
* For the SPSR_ELx layout for AArch32 seen from AArch64, see:
* - ARM DDI 0487E.a, page C5-426
*
* Here we manipulate the fields in order of the AArch32 SPSR_ELx layout, from
* MSB to LSB.
*/
static unsigned long get_except32_cpsr(struct kvm_vcpu *vcpu, u32 mode)
{
u32 sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
unsigned long old, new;
old = *vcpu_cpsr(vcpu);
new = 0;
new |= (old & PSR_AA32_N_BIT);
new |= (old & PSR_AA32_Z_BIT);
new |= (old & PSR_AA32_C_BIT);
new |= (old & PSR_AA32_V_BIT);
new |= (old & PSR_AA32_Q_BIT);
// CPSR.IT[7:0] are set to zero upon any exception
// See ARM DDI 0487E.a, section G1.12.3
// See ARM DDI 0406C.d, section B1.8.3
new |= (old & PSR_AA32_DIT_BIT);
// CPSR.SSBS is set to SCTLR.DSSBS upon any exception
// See ARM DDI 0487E.a, page G8-6244
if (sctlr & BIT(31))
new |= PSR_AA32_SSBS_BIT;
// CPSR.PAN is unchanged unless SCTLR.SPAN == 0b0
// SCTLR.SPAN is RES1 when ARMv8.1-PAN is not implemented
// See ARM DDI 0487E.a, page G8-6246
new |= (old & PSR_AA32_PAN_BIT);
if (!(sctlr & BIT(23)))
new |= PSR_AA32_PAN_BIT;
// SS does not exist in AArch32, so ignore
// CPSR.IL is set to zero upon any exception
// See ARM DDI 0487E.a, page G1-5527
new |= (old & PSR_AA32_GE_MASK);
// CPSR.IT[7:0] are set to zero upon any exception
// See prior comment above
// CPSR.E is set to SCTLR.EE upon any exception
// See ARM DDI 0487E.a, page G8-6245
// See ARM DDI 0406C.d, page B4-1701
if (sctlr & BIT(25))
new |= PSR_AA32_E_BIT;
// CPSR.A is unchanged upon an exception to Undefined, Supervisor
// CPSR.A is set upon an exception to other modes
// See ARM DDI 0487E.a, pages G1-5515 to G1-5516
// See ARM DDI 0406C.d, page B1-1182
new |= (old & PSR_AA32_A_BIT);
if (mode != PSR_AA32_MODE_UND && mode != PSR_AA32_MODE_SVC)
new |= PSR_AA32_A_BIT;
// CPSR.I is set upon any exception
// See ARM DDI 0487E.a, pages G1-5515 to G1-5516
// See ARM DDI 0406C.d, page B1-1182
new |= PSR_AA32_I_BIT;
// CPSR.F is set upon an exception to FIQ
// CPSR.F is unchanged upon an exception to other modes
// See ARM DDI 0487E.a, pages G1-5515 to G1-5516
// See ARM DDI 0406C.d, page B1-1182
new |= (old & PSR_AA32_F_BIT);
if (mode == PSR_AA32_MODE_FIQ)
new |= PSR_AA32_F_BIT;
// CPSR.T is set to SCTLR.TE upon any exception
// See ARM DDI 0487E.a, page G8-5514
// See ARM DDI 0406C.d, page B1-1181
if (sctlr & BIT(30))
new |= PSR_AA32_T_BIT;
new |= mode;
return new;
}
/*
* Table taken from ARMv8 ARM DDI0487B-B, table G1-10.
*/
static const u8 return_offsets[8][2] = {
[0] = { 0, 0 }, /* Reset, unused */
[1] = { 4, 2 }, /* Undefined */
[2] = { 0, 0 }, /* SVC, unused */
[3] = { 4, 4 }, /* Prefetch abort */
[4] = { 8, 8 }, /* Data abort */
[5] = { 0, 0 }, /* HVC, unused */
[6] = { 4, 4 }, /* IRQ, unused */
[7] = { 4, 4 }, /* FIQ, unused */
};
static void enter_exception32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
{
unsigned long spsr = *vcpu_cpsr(vcpu);
bool is_thumb = (spsr & PSR_AA32_T_BIT);
u32 sctlr = __vcpu_read_sys_reg(vcpu, SCTLR_EL1);
u32 return_address;
*vcpu_cpsr(vcpu) = get_except32_cpsr(vcpu, mode);
return_address = *vcpu_pc(vcpu);
return_address += return_offsets[vect_offset >> 2][is_thumb];
/* KVM only enters the ABT and UND modes, so only deal with those */
switch(mode) {
case PSR_AA32_MODE_ABT:
__vcpu_write_spsr_abt(vcpu, host_spsr_to_spsr32(spsr));
vcpu_gp_regs(vcpu)->compat_lr_abt = return_address;
break;
case PSR_AA32_MODE_UND:
__vcpu_write_spsr_und(vcpu, host_spsr_to_spsr32(spsr));
vcpu_gp_regs(vcpu)->compat_lr_und = return_address;
break;
}
/* Branch to exception vector */
if (sctlr & (1 << 13))
vect_offset += 0xffff0000;
else /* always have security exceptions */
vect_offset += __vcpu_read_sys_reg(vcpu, VBAR_EL1);
*vcpu_pc(vcpu) = vect_offset;
}
static void kvm_inject_exception(struct kvm_vcpu *vcpu)
{
if (vcpu_el1_is_32bit(vcpu)) {
switch (vcpu_get_flag(vcpu, EXCEPT_MASK)) {
case unpack_vcpu_flag(EXCEPT_AA32_UND):
enter_exception32(vcpu, PSR_AA32_MODE_UND, 4);
break;
case unpack_vcpu_flag(EXCEPT_AA32_IABT):
enter_exception32(vcpu, PSR_AA32_MODE_ABT, 12);
break;
case unpack_vcpu_flag(EXCEPT_AA32_DABT):
enter_exception32(vcpu, PSR_AA32_MODE_ABT, 16);
break;
default:
/* Err... */
break;
}
} else {
switch (vcpu_get_flag(vcpu, EXCEPT_MASK)) {
case unpack_vcpu_flag(EXCEPT_AA64_EL1_SYNC):
enter_exception64(vcpu, PSR_MODE_EL1h, except_type_sync);
break;
case unpack_vcpu_flag(EXCEPT_AA64_EL1_SERR):
enter_exception64(vcpu, PSR_MODE_EL1h, except_type_serror);
break;
case unpack_vcpu_flag(EXCEPT_AA64_EL2_SYNC):
enter_exception64(vcpu, PSR_MODE_EL2h, except_type_sync);
break;
case unpack_vcpu_flag(EXCEPT_AA64_EL2_IRQ):
enter_exception64(vcpu, PSR_MODE_EL2h, except_type_irq);
break;
case unpack_vcpu_flag(EXCEPT_AA64_EL2_SERR):
enter_exception64(vcpu, PSR_MODE_EL2h, except_type_serror);
break;
default:
/*
* Only EL1_{SYNC,SERR} and EL2_{SYNC,IRQ,SERR} makes
* sense so far. Everything else gets silently
* ignored.
*/
break;
}
}
}
/*
* Adjust the guest PC (and potentially exception state) depending on
* flags provided by the emulation code.
*/
void __kvm_adjust_pc(struct kvm_vcpu *vcpu)
{
if (vcpu_get_flag(vcpu, PENDING_EXCEPTION)) {
kvm_inject_exception(vcpu);
vcpu_clear_flag(vcpu, PENDING_EXCEPTION);
vcpu_clear_flag(vcpu, EXCEPT_MASK);
} else if (vcpu_get_flag(vcpu, INCREMENT_PC)) {
kvm_skip_instr(vcpu);
vcpu_clear_flag(vcpu, INCREMENT_PC);
}
}
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