Commit a3725973 authored by Rik van Riel's avatar Rik van Riel Committed by Ingo Molnar
Browse files

x86/mm: Make MMU_GATHER_RCU_TABLE_FREE unconditional 



Currently x86 uses CONFIG_MMU_GATHER_TABLE_FREE when using
paravirt, and not when running on bare metal.

There is no real good reason to do things differently for
each setup. Make them all the same.

Currently get_user_pages_fast synchronizes against page table
freeing in two different ways:

 - on bare metal, by blocking IRQs, which block TLB flush IPIs
 - on paravirt, with MMU_GATHER_RCU_TABLE_FREE

This is done because some paravirt TLB flush implementations
handle the TLB flush in the hypervisor, and will do the flush
even when the target CPU has interrupts disabled.

Always handle page table freeing with MMU_GATHER_RCU_TABLE_FREE.
Using RCU synchronization between page table freeing and get_user_pages_fast()
allows bare metal to also do TLB flushing while interrupts are disabled.

Various places in the mm do still block IRQs or disable preemption
as an implicit way to block RCU frees.

That makes it safe to use INVLPGB on AMD CPUs.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarRik van Riel <riel@surriel.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Tested-by: default avatarManali Shukla <Manali.Shukla@amd.com>
Tested-by: default avatarBrendan Jackman <jackmanb@google.com>
Tested-by: default avatarMichael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250213161423.449435-2-riel@surriel.com
parent 282f3952

arch/x86/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -278,7 +278,7 @@ config X86 
	select HAVE_PCI

	select HAVE_PERF_REGS

	select HAVE_PERF_USER_STACK_DUMP

	select MMU_GATHER_RCU_TABLE_FREE	if PARAVIRT

	select MMU_GATHER_RCU_TABLE_FREE

	select MMU_GATHER_MERGE_VMAS

	select HAVE_POSIX_CPU_TIMERS_TASK_WORK

	select HAVE_REGS_AND_STACK_ACCESS_API

arch/x86/kernel/paravirt.c

+1 −16
Original line number Diff line number Diff line
@@ -59,21 +59,6 @@ void __init native_pv_lock_init(void) 
		static_branch_enable(&virt_spin_lock_key);

}



#ifndef CONFIG_PT_RECLAIM

static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)

{

	struct ptdesc *ptdesc = (struct ptdesc *)table;



	pagetable_dtor(ptdesc);

	tlb_remove_page(tlb, ptdesc_page(ptdesc));

}

#else

static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)

{

	tlb_remove_table(tlb, table);

}

#endif



struct static_key paravirt_steal_enabled;

struct static_key paravirt_steal_rq_enabled;
@@ -195,7 +180,7 @@ struct paravirt_patch_template pv_ops = { 
	.mmu.flush_tlb_kernel	= native_flush_tlb_global,

	.mmu.flush_tlb_one_user	= native_flush_tlb_one_user,

	.mmu.flush_tlb_multi	= native_flush_tlb_multi,

	.mmu.tlb_remove_table	= native_tlb_remove_table,

	.mmu.tlb_remove_table	= tlb_remove_table,



	.mmu.exit_mmap		= paravirt_nop,

	.mmu.notify_page_enc_status_changed	= paravirt_nop,

arch/x86/mm/pgtable.c

+4 −23
Original line number Diff line number Diff line
@@ -18,25 +18,6 @@ EXPORT_SYMBOL(physical_mask); 
#define PGTABLE_HIGHMEM 0

#endif



#ifndef CONFIG_PARAVIRT

#ifndef CONFIG_PT_RECLAIM

static inline

void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)

{

	struct ptdesc *ptdesc = (struct ptdesc *)table;



	pagetable_dtor(ptdesc);

	tlb_remove_page(tlb, ptdesc_page(ptdesc));

}

#else

static inline

void paravirt_tlb_remove_table(struct mmu_gather *tlb, void *table)

{

	tlb_remove_table(tlb, table);

}

#endif /* !CONFIG_PT_RECLAIM */

#endif /* !CONFIG_PARAVIRT */



gfp_t __userpte_alloc_gfp = GFP_PGTABLE_USER | PGTABLE_HIGHMEM;



pgtable_t pte_alloc_one(struct mm_struct *mm)
@@ -64,7 +45,7 @@ early_param("userpte", setup_userpte); 
void ___pte_free_tlb(struct mmu_gather *tlb, struct page *pte)

{

	paravirt_release_pte(page_to_pfn(pte));

	paravirt_tlb_remove_table(tlb, page_ptdesc(pte));

	tlb_remove_table(tlb, page_ptdesc(pte));

}



#if CONFIG_PGTABLE_LEVELS > 2
@@ -78,21 +59,21 @@ void ___pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd) 
#ifdef CONFIG_X86_PAE

	tlb->need_flush_all = 1;

#endif

	paravirt_tlb_remove_table(tlb, virt_to_ptdesc(pmd));

	tlb_remove_table(tlb, virt_to_ptdesc(pmd));

}



#if CONFIG_PGTABLE_LEVELS > 3

void ___pud_free_tlb(struct mmu_gather *tlb, pud_t *pud)

{

	paravirt_release_pud(__pa(pud) >> PAGE_SHIFT);

	paravirt_tlb_remove_table(tlb, virt_to_ptdesc(pud));

	tlb_remove_table(tlb, virt_to_ptdesc(pud));

}



#if CONFIG_PGTABLE_LEVELS > 4

void ___p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d)

{

	paravirt_release_p4d(__pa(p4d) >> PAGE_SHIFT);

	paravirt_tlb_remove_table(tlb, virt_to_ptdesc(p4d));

	tlb_remove_table(tlb, virt_to_ptdesc(p4d));

}

#endif	/* CONFIG_PGTABLE_LEVELS > 4 */

#endif	/* CONFIG_PGTABLE_LEVELS > 3 */