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x86/alternatives: Remove the confusing, inaccurate & unnecessary 'temp_mm_state_t' abstraction

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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 <mingo@kernel.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250411054105.2341982-14-mingo@kernel.org
This commit is contained in:
Ingo Molnar
2025-04-11 07:40:25 +02:00
parent 5224f09a7b
commit f5afa2e8ef
1 changed files with 10 additions and 14 deletions
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24
arch/x86/kernel/alternative.c
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@@ -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