From: Ingo Molnar Date: Fri, 11 Apr 2025 05:40:25 +0000 (+0200) Subject: x86/alternatives: Remove the confusing, inaccurate & unnecessary 'temp_mm_state_t... X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=f5afa2e8efda592ecc69cea7528ff660ac1d8096;p=users%2Fdwmw2%2Flinux.git x86/alternatives: Remove the confusing, inaccurate & unnecessary 'temp_mm_state_t' abstraction So the temp_mm_state_t abstraction used by use_temporary_mm() and unuse_temporary_mm() is super confusing: - The whole machinery is about temporarily switching to the text_poke_mm utility MM that got allocated during bootup for text-patching purposes alone: temp_mm_state_t prev; /* * Loading the temporary mm behaves as a compiler barrier, which * guarantees that the PTE will be set at the time memcpy() is done. */ prev = use_temporary_mm(text_poke_mm); - Yet the value that gets saved in the temp_mm_state_t variable is not the temporary MM ... but the previous MM... - Ie. we temporarily put the non-temporary MM into a variable that has the temp_mm_state_t type. This makes no sense whatsoever. - The confusion continues in unuse_temporary_mm(): static inline void unuse_temporary_mm(temp_mm_state_t prev_state) Here we unuse an MM that is ... not the temporary MM, but the previous MM. :-/ Fix up all this confusion by removing the unnecessary layer of abstraction and using a bog-standard 'struct mm_struct *prev_mm' variable to save the MM to. Signed-off-by: Ingo Molnar Cc: Juergen Gross Cc: "H . Peter Anvin" Cc: Linus Torvalds Cc: Peter Zijlstra Link: https://lore.kernel.org/r/20250411054105.2341982-14-mingo@kernel.org --- diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index b8794f756ea4a..0ee43aa70adfe 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -2139,10 +2139,6 @@ void __init_or_module text_poke_early(void *addr, const void *opcode, } } -typedef struct { - struct mm_struct *mm; -} temp_mm_state_t; - /* * Using a temporary mm allows to set temporary mappings that are not accessible * by other CPUs. Such mappings are needed to perform sensitive memory writes @@ -2156,9 +2152,9 @@ typedef struct { * loaded, thereby preventing interrupt handler bugs from overriding * the kernel memory protection. */ -static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) +static inline struct mm_struct *use_temporary_mm(struct mm_struct *temp_mm) { - temp_mm_state_t temp_state; + struct mm_struct *prev_mm; lockdep_assert_irqs_disabled(); @@ -2170,8 +2166,8 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) if (this_cpu_read(cpu_tlbstate_shared.is_lazy)) leave_mm(); - temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); - switch_mm_irqs_off(NULL, mm, current); + prev_mm = this_cpu_read(cpu_tlbstate.loaded_mm); + switch_mm_irqs_off(NULL, temp_mm, current); /* * If breakpoints are enabled, disable them while the temporary mm is @@ -2187,17 +2183,17 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) if (hw_breakpoint_active()) hw_breakpoint_disable(); - return temp_state; + return prev_mm; } __ro_after_init struct mm_struct *text_poke_mm; __ro_after_init unsigned long text_poke_mm_addr; -static inline void unuse_temporary_mm(temp_mm_state_t prev_state) +static inline void unuse_temporary_mm(struct mm_struct *prev_mm) { lockdep_assert_irqs_disabled(); - switch_mm_irqs_off(NULL, prev_state.mm, current); + switch_mm_irqs_off(NULL, prev_mm, current); /* Clear the cpumask, to indicate no TLB flushing is needed anywhere */ cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(text_poke_mm)); @@ -2228,7 +2224,7 @@ static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t l { bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE; struct page *pages[2] = {NULL}; - temp_mm_state_t prev; + struct mm_struct *prev_mm; unsigned long flags; pte_t pte, *ptep; spinlock_t *ptl; @@ -2286,7 +2282,7 @@ static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t l * Loading the temporary mm behaves as a compiler barrier, which * guarantees that the PTE will be set at the time memcpy() is done. */ - prev = use_temporary_mm(text_poke_mm); + prev_mm = use_temporary_mm(text_poke_mm); kasan_disable_current(); func((u8 *)text_poke_mm_addr + offset_in_page(addr), src, len); @@ -2307,7 +2303,7 @@ static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t l * instruction that already allows the core to see the updated version. * Xen-PV is assumed to serialize execution in a similar manner. */ - unuse_temporary_mm(prev); + unuse_temporary_mm(prev_mm); /* * Flushing the TLB might involve IPIs, which would require enabled