Re: [RFC PATCH v3 2/7] mm/asi: ASI entry/exit interface

[Ira Weiny]

On Wed, Feb 26, 2020 at 05:21:55PM +0100, Alexandre Chartre wrote:
> Address Space Isolation (ASI) is entered by calling asi_enter() which
> switches the kernel page-table to the ASI page-table. Isolation is then
> exited by calling asi_exit() which switches the page-table back to the
> original kernel page-table.
> 
> The ASI being used and its state is tracked in a per-cpu ASI session
> structure (struct asi_session).
> 
> Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/asi.h         |    4 ++
>  arch/x86/include/asm/asi_session.h |   17 +++++++
>  arch/x86/include/asm/mmu_context.h |   19 +++++++-
>  arch/x86/include/asm/tlbflush.h    |   12 +++++
>  arch/x86/mm/asi.c                  |   90 ++++++++++++++++++++++++++++++++++++
>  5 files changed, 140 insertions(+), 2 deletions(-)
>  create mode 100644 arch/x86/include/asm/asi_session.h
> 
> diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
> index 844a81f..29b745a 100644
> --- a/arch/x86/include/asm/asi.h
> +++ b/arch/x86/include/asm/asi.h
> @@ -44,6 +44,8 @@
>  
>  #include <linux/export.h>
>  
> +#include <asm/asi_session.h>
> +
>  struct asi_type {
>  	int			pcid_prefix;	/* PCID prefix */
>  };
> @@ -80,6 +82,8 @@ struct asi {
>  extern struct asi *asi_create(struct asi_type *type);
>  extern void asi_destroy(struct asi *asi);
>  extern void asi_set_pagetable(struct asi *asi, pgd_t *pagetable);
> +extern int asi_enter(struct asi *asi);
> +extern void asi_exit(struct asi *asi);
>  
>  #endif	/* __ASSEMBLY__ */
>  
> diff --git a/arch/x86/include/asm/asi_session.h b/arch/x86/include/asm/asi_session.h
> new file mode 100644
> index 0000000..9d39c93
> --- /dev/null
> +++ b/arch/x86/include/asm/asi_session.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef ARCH_X86_MM_ASI_SESSION_H
> +#define ARCH_X86_MM_ASI_SESSION_H
> +
> +#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
> +
> +struct asi;
> +
> +struct asi_session {
> +	struct asi		*asi;		/* ASI for this session */
> +	unsigned long		isolation_cr3;	/* cr3 when ASI is active */
> +	unsigned long		original_cr3;	/* cr3 before entering ASI */
> +};
> +
> +#endif	/* CONFIG_ADDRESS_SPACE_ISOLATION */
> +
> +#endif
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 5f33924..2d65443 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -14,6 +14,7 @@
>  #include <asm/paravirt.h>
>  #include <asm/mpx.h>
>  #include <asm/debugreg.h>
> +#include <asm/asi.h>
>  
>  extern atomic64_t last_mm_ctx_id;
>  
> @@ -349,8 +350,22 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
>   */
>  static inline unsigned long __get_current_cr3_fast(void)
>  {
> -	unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
> -		this_cpu_read(cpu_tlbstate.loaded_mm_asid));
> +	unsigned long cr3;
> +
> +	/*
> +	 * If isolation is active then we need to return the CR3 for the
> +	 * currently active ASI. This value is stored in the isolation_cr3
> +	 * field of the ASI session.
> +	 */
> +	if (IS_ENABLED(CONFIG_ADDRESS_SPACE_ISOLATION) &&
> +	    this_cpu_read(cpu_asi_session.asi)) {
> +		cr3 = this_cpu_read(cpu_asi_session.isolation_cr3);
> +		/* CR3 read never returns with the NOFLUSH bit */
> +		cr3 &= ~X86_CR3_PCID_NOFLUSH;
> +	} else {
> +		cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
> +				this_cpu_read(cpu_tlbstate.loaded_mm_asid));
> +	}
>  
>  	/* For now, be very restrictive about when this can be called. */
>  	VM_WARN_ON(in_nmi() || preemptible());
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 6f66d84..241058f 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -12,6 +12,7 @@
>  #include <asm/invpcid.h>
>  #include <asm/pti.h>
>  #include <asm/processor-flags.h>
> +#include <asm/asi.h>
>  
>  /*
>   * The x86 feature is called PCID (Process Context IDentifier). It is similar
> @@ -239,9 +240,20 @@ struct tlb_state {
>  	 * context 0.
>  	 */
>  	struct tlb_context ctxs[TLB_NR_DYN_ASIDS];
> +
> +#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
> +	/*
> +	 * The ASI session tracks the ASI being used and its state.
> +	 */
> +	struct asi_session asi_session;
> +#endif
>  };
>  DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
>  
> +#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
> +#define cpu_asi_session	(cpu_tlbstate.asi_session)
> +#endif
> +
>  /*
>   * Blindly accessing user memory from NMI context can be dangerous
>   * if we're in the middle of switching the current user task or
> diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
> index 0a0ac9d..9fbc921 100644
> --- a/arch/x86/mm/asi.c
> +++ b/arch/x86/mm/asi.c
> @@ -10,6 +10,8 @@
>  
>  #include <asm/asi.h>
>  #include <asm/bug.h>
> +#include <asm/mmu_context.h>
> +#include <asm/tlbflush.h>
>  
>  struct asi *asi_create(struct asi_type *type)
>  {
> @@ -58,3 +60,91 @@ void asi_set_pagetable(struct asi *asi, pgd_t *pagetable)
>  
>  }
>  EXPORT_SYMBOL(asi_set_pagetable);
> +
> +static void asi_switch_to_asi_cr3(struct asi *asi)
> +{
> +	unsigned long original_cr3, asi_cr3;
> +	struct asi_session *asi_session;
> +	u16 pcid;
> +
> +	WARN_ON(!irqs_disabled());
> +
> +	original_cr3 = __get_current_cr3_fast();
> +
> +	/* build the ASI cr3 value */
> +	asi_cr3 = asi->base_cr3;
> +	if (boot_cpu_has(X86_FEATURE_PCID)) {
> +		pcid = original_cr3 & ASI_KERNEL_PCID_MASK;
> +		asi_cr3 |= pcid;
> +	}
> +
> +	/* get the ASI session ready for entering ASI */
> +	asi_session = &get_cpu_var(cpu_asi_session);
> +	asi_session->asi = asi;
> +	asi_session->original_cr3 = original_cr3;
> +	asi_session->isolation_cr3 = asi_cr3;
> +
> +	/* Update CR3 to immediately enter ASI */
> +	native_write_cr3(asi_cr3);
> +}
> +
> +static void asi_switch_to_kernel_cr3(struct asi *asi)

asi is not used in this function?

> +{
> +	struct asi_session *asi_session;
> +	unsigned long original_cr3;
> +
> +	WARN_ON(!irqs_disabled());
> +
> +	original_cr3 = this_cpu_read(cpu_asi_session.original_cr3);
> +	if (boot_cpu_has(X86_FEATURE_PCID))
> +		original_cr3 |= X86_CR3_PCID_NOFLUSH;
> +	native_write_cr3(original_cr3);
> +
> +	asi_session = &get_cpu_var(cpu_asi_session);
> +	asi_session->asi = NULL;
> +}
> +
> +int asi_enter(struct asi *asi)
> +{
> +	struct asi *current_asi;
> +	unsigned long flags;
> +
> +	/*
> +	 * We can re-enter isolation, but only with the same ASI (we don't
> +	 * support nesting isolation).
> +	 */
> +	current_asi = this_cpu_read(cpu_asi_session.asi);
> +	if (current_asi) {
> +		if (current_asi != asi) {
> +			WARN_ON(1);
> +			return -EBUSY;
> +		}

if (WARN_ON(current_asi != asi)) {
	return -EBUSY;

???

Ira

> +		return 0;
> +	}
> +
> +	local_irq_save(flags);
> +	asi_switch_to_asi_cr3(asi);
> +	local_irq_restore(flags);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(asi_enter);
> +
> +void asi_exit(struct asi *asi)
> +{
> +	struct asi *current_asi;
> +	unsigned long flags;
> +
> +	current_asi = this_cpu_read(cpu_asi_session.asi);
> +	if (!current_asi) {
> +		/* already exited */
> +		return;
> +	}
> +
> +	WARN_ON(current_asi != asi);
> +
> +	local_irq_save(flags);
> +	asi_switch_to_kernel_cr3(asi);
> +	local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL(asi_exit);
> -- 
> 1.7.1
> 
>