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/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/kernel.h>
#include <asm/desc.h>
#include <asm/fred.h>
#include <asm/tlbflush.h>
#include <asm/traps.h>
/* #DB in the kernel would imply the use of a kernel debugger. */
#define FRED_DB_STACK_LEVEL 1UL
#define FRED_NMI_STACK_LEVEL 2UL
#define FRED_MC_STACK_LEVEL 2UL
/*
* #DF is the highest level because a #DF means "something went wrong
* *while delivering an exception*." The number of cases for which that
* can happen with FRED is drastically reduced and basically amounts to
* "the stack you pointed me to is broken." Thus, always change stacks
* on #DF, which means it should be at the highest level.
*/
#define FRED_DF_STACK_LEVEL 3UL
#define FRED_STKLVL(vector, lvl) ((lvl) << (2 * (vector)))
DEFINE_PER_CPU(unsigned long, fred_rsp0);
EXPORT_PER_CPU_SYMBOL(fred_rsp0);
void cpu_init_fred_exceptions(void)
{
/* When FRED is enabled by default, remove this log message */
pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
/*
* If a kernel event is delivered before a CPU goes to user level for
* the first time, its SS is NULL thus NULL is pushed into the SS field
* of the FRED stack frame. But before ERETS is executed, the CPU may
* context switch to another task and go to user level. Then when the
* CPU comes back to kernel mode, SS is changed to __KERNEL_DS. Later
* when ERETS is executed to return from the kernel event handler, a #GP
* fault is generated because SS doesn't match the SS saved in the FRED
* stack frame.
*
* Initialize SS to __KERNEL_DS when enabling FRED to avoid such #GPs.
*/
loadsegment(ss, __KERNEL_DS);
wrmsrl(MSR_IA32_FRED_CONFIG,
/* Reserve for CALL emulation */
FRED_CONFIG_REDZONE |
FRED_CONFIG_INT_STKLVL(0) |
FRED_CONFIG_ENTRYPOINT(asm_fred_entrypoint_user));
wrmsrl(MSR_IA32_FRED_STKLVLS, 0);
wrmsrl(MSR_IA32_FRED_RSP0, 0);
wrmsrl(MSR_IA32_FRED_RSP1, 0);
wrmsrl(MSR_IA32_FRED_RSP2, 0);
wrmsrl(MSR_IA32_FRED_RSP3, 0);
/* Enable FRED */
cr4_set_bits(X86_CR4_FRED);
/* Any further IDT use is a bug */
idt_invalidate();
/* Use int $0x80 for 32-bit system calls in FRED mode */
setup_clear_cpu_cap(X86_FEATURE_SYSENTER32);
setup_clear_cpu_cap(X86_FEATURE_SYSCALL32);
}
/* Must be called after setup_cpu_entry_areas() */
void cpu_init_fred_rsps(void)
{
/*
* The purpose of separate stacks for NMI, #DB and #MC *in the kernel*
* (remember that user space faults are always taken on stack level 0)
* is to avoid overflowing the kernel stack.
*/
wrmsrl(MSR_IA32_FRED_STKLVLS,
FRED_STKLVL(X86_TRAP_DB, FRED_DB_STACK_LEVEL) |
FRED_STKLVL(X86_TRAP_NMI, FRED_NMI_STACK_LEVEL) |
FRED_STKLVL(X86_TRAP_MC, FRED_MC_STACK_LEVEL) |
FRED_STKLVL(X86_TRAP_DF, FRED_DF_STACK_LEVEL));
/* The FRED equivalents to IST stacks... */
wrmsrl(MSR_IA32_FRED_RSP1, __this_cpu_ist_top_va(DB));
wrmsrl(MSR_IA32_FRED_RSP2, __this_cpu_ist_top_va(NMI));
wrmsrl(MSR_IA32_FRED_RSP3, __this_cpu_ist_top_va(DF));
}
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