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The FRED RSP0 MSR points to the top of the kernel stack for user level event delivery. As this is the task stack it needs to be updated when a task is scheduled in. The update is done at context switch. That means it's also done when switching to kernel threads, which is pointless as those never go out to user space. For KVM threads this means there are two writes to FRED_RSP0 as KVM has to switch to the guest value before VMENTER. Defer the update to the exit to user space path and cache the per CPU FRED_RSP0 value, so redundant writes can be avoided. Provide fred_sync_rsp0() for KVM to keep the cache in sync with the actual MSR value after returning from guest to host mode. [ tglx: Massage change log ] Suggested-by: Sean Christopherson <seanjc@google.com> Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Xin Li (Intel) <xin@zytor.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/all/20240822073906.2176342-4-xin@zytor.com
119 lines
3.2 KiB
C
119 lines
3.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Macros for Flexible Return and Event Delivery (FRED)
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*/
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#ifndef ASM_X86_FRED_H
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#define ASM_X86_FRED_H
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#include <linux/const.h>
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#include <asm/asm.h>
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#include <asm/trapnr.h>
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/*
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* FRED event return instruction opcodes for ERET{S,U}; supported in
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* binutils >= 2.41.
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*/
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#define ERETS _ASM_BYTES(0xf2,0x0f,0x01,0xca)
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#define ERETU _ASM_BYTES(0xf3,0x0f,0x01,0xca)
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/*
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* RSP is aligned to a 64-byte boundary before used to push a new stack frame
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*/
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#define FRED_STACK_FRAME_RSP_MASK _AT(unsigned long, (~0x3f))
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/*
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* Used for the return address for call emulation during code patching,
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* and measured in 64-byte cache lines.
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*/
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#define FRED_CONFIG_REDZONE_AMOUNT 1
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#define FRED_CONFIG_REDZONE (_AT(unsigned long, FRED_CONFIG_REDZONE_AMOUNT) << 6)
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#define FRED_CONFIG_INT_STKLVL(l) (_AT(unsigned long, l) << 9)
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#define FRED_CONFIG_ENTRYPOINT(p) _AT(unsigned long, (p))
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#ifndef __ASSEMBLY__
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#ifdef CONFIG_X86_FRED
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#include <linux/kernel.h>
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#include <linux/sched/task_stack.h>
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#include <asm/ptrace.h>
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struct fred_info {
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/* Event data: CR2, DR6, ... */
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unsigned long edata;
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unsigned long resv;
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};
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/* Full format of the FRED stack frame */
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struct fred_frame {
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struct pt_regs regs;
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struct fred_info info;
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};
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static __always_inline struct fred_info *fred_info(struct pt_regs *regs)
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{
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return &container_of(regs, struct fred_frame, regs)->info;
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}
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static __always_inline unsigned long fred_event_data(struct pt_regs *regs)
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{
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return fred_info(regs)->edata;
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}
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void asm_fred_entrypoint_user(void);
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void asm_fred_entrypoint_kernel(void);
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void asm_fred_entry_from_kvm(struct fred_ss);
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__visible void fred_entry_from_user(struct pt_regs *regs);
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__visible void fred_entry_from_kernel(struct pt_regs *regs);
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__visible void __fred_entry_from_kvm(struct pt_regs *regs);
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/* Can be called from noinstr code, thus __always_inline */
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static __always_inline void fred_entry_from_kvm(unsigned int type, unsigned int vector)
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{
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struct fred_ss ss = {
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.ss =__KERNEL_DS,
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.type = type,
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.vector = vector,
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.nmi = type == EVENT_TYPE_NMI,
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.lm = 1,
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};
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asm_fred_entry_from_kvm(ss);
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}
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void cpu_init_fred_exceptions(void);
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void cpu_init_fred_rsps(void);
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void fred_complete_exception_setup(void);
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DECLARE_PER_CPU(unsigned long, fred_rsp0);
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static __always_inline void fred_sync_rsp0(unsigned long rsp0)
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{
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__this_cpu_write(fred_rsp0, rsp0);
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}
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static __always_inline void fred_update_rsp0(void)
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{
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unsigned long rsp0 = (unsigned long) task_stack_page(current) + THREAD_SIZE;
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if (cpu_feature_enabled(X86_FEATURE_FRED) && (__this_cpu_read(fred_rsp0) != rsp0)) {
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wrmsrns(MSR_IA32_FRED_RSP0, rsp0);
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__this_cpu_write(fred_rsp0, rsp0);
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}
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}
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#else /* CONFIG_X86_FRED */
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static __always_inline unsigned long fred_event_data(struct pt_regs *regs) { return 0; }
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static inline void cpu_init_fred_exceptions(void) { }
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static inline void cpu_init_fred_rsps(void) { }
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static inline void fred_complete_exception_setup(void) { }
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static inline void fred_entry_from_kvm(unsigned int type, unsigned int vector) { }
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static inline void fred_sync_rsp0(unsigned long rsp0) { }
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static inline void fred_update_rsp0(void) { }
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#endif /* CONFIG_X86_FRED */
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#endif /* !__ASSEMBLY__ */
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#endif /* ASM_X86_FRED_H */
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