Date: Wed, 24 Sep 2025 13:02:47 GMT From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: a31969687545 - main - amd64: add wrmsr_early_safe(9) Message-ID: <202509241302.58OD2lKo034437@gitrepo.freebsd.org>
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The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=a319696875451229f492b6c15e58a0ac54dbcda1 commit a319696875451229f492b6c15e58a0ac54dbcda1 Author: Konstantin Belousov <kib@FreeBSD.org> AuthorDate: 2025-09-18 21:55:19 +0000 Commit: Konstantin Belousov <kib@FreeBSD.org> CommitDate: 2025-09-24 13:02:27 +0000 amd64: add wrmsr_early_safe(9) The variant of wrmsr_safe(9) that might work before IDT and curpcb are initialized. Assumes BSP, and that all APs are parked. Before calling wrmsr_early_safe(), the wrmsr_early_safe_start() should be called, afterward wrmsr_early_safe_end() restores the bootenv IDT. Reviewed by: markj Tested by: glebius Sponsored by: The FreeBSD Foundation MFC after: 1 week Differential revision: https://reviews.freebsd.org/D52607 --- sys/amd64/amd64/machdep.c | 33 +++++++++++++++++++++++++++++++++ sys/amd64/amd64/support.S | 16 ++++++++++++++++ sys/amd64/include/md_var.h | 4 ++++ 3 files changed, 53 insertions(+) diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c index 9ff60439d1ec..2fce1a7e64b6 100644 --- a/sys/amd64/amd64/machdep.c +++ b/sys/amd64/amd64/machdep.c @@ -1822,6 +1822,39 @@ clear_pcb_flags(struct pcb *pcb, const u_int flags) : "cc", "memory"); } +extern const char wrmsr_early_safe_gp_handler[]; +static struct region_descriptor wrmsr_early_safe_orig_efi_idt; + +void +wrmsr_early_safe_start(void) +{ + struct region_descriptor efi_idt; + struct gate_descriptor *gpf_descr; + + sidt(&wrmsr_early_safe_orig_efi_idt); + efi_idt.rd_limit = 32 * sizeof(idt0[0]); + efi_idt.rd_base = (uintptr_t)idt0; + lidt(&efi_idt); + + gpf_descr = &idt0[IDT_GP]; + gpf_descr->gd_looffset = (uintptr_t)wrmsr_early_safe_gp_handler; + gpf_descr->gd_hioffset = (uintptr_t)wrmsr_early_safe_gp_handler >> 16; + gpf_descr->gd_selector = rcs(); + gpf_descr->gd_type = SDT_SYSTGT; + gpf_descr->gd_p = 1; +} + +void +wrmsr_early_safe_end(void) +{ + struct gate_descriptor *gpf_descr; + + lidt(&wrmsr_early_safe_orig_efi_idt); + + gpf_descr = &idt0[IDT_GP]; + memset(gpf_descr, 0, sizeof(*gpf_descr)); +} + #ifdef KDB /* diff --git a/sys/amd64/amd64/support.S b/sys/amd64/amd64/support.S index 870cd255abb7..27694a95653c 100644 --- a/sys/amd64/amd64/support.S +++ b/sys/amd64/amd64/support.S @@ -1565,6 +1565,22 @@ msr_onfault: POP_FRAME_POINTER ret +ENTRY(wrmsr_early_safe) + movl %edi,%ecx + movl %esi,%eax + sarq $32,%rsi + movl %esi,%edx + wrmsr + xorl %eax,%eax +wrmsr_early_faulted: + ret + +ENTRY(wrmsr_early_safe_gp_handler) + addq $8,%rsp + movl $EFAULT,%eax + movq $wrmsr_early_faulted,(%rsp) + iretq + /* * void pmap_pti_pcid_invalidate(uint64_t ucr3, uint64_t kcr3); * Invalidates address space addressed by ucr3, then returns to kcr3. diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h index b6ddc6eaaebe..b6d8c469cdf6 100644 --- a/sys/amd64/include/md_var.h +++ b/sys/amd64/include/md_var.h @@ -99,6 +99,10 @@ void get_fpcontext(struct thread *td, struct __mcontext *mcp, int set_fpcontext(struct thread *td, struct __mcontext *mcp, char *xfpustate, size_t xfpustate_len); +void wrmsr_early_safe_start(void); +void wrmsr_early_safe_end(void); +int wrmsr_early_safe(u_int msr, uint64_t data); + #endif /* !_MACHINE_MD_VAR_H_ */ #endif /* __i386__ */
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