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Subject[RFC PATCH v3 4/7] mm/asi: Interrupt ASI on interrupt/exception/NMI
Date
If an interrupt/exception/NMI is triggered while using ASI then
ASI is interrupted and the system switches back to the (kernel)
page-table used before entering ASI.

When the interrupt/exception/NMI handler returns then ASI is
resumed by switching back to the ASI page-table.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
arch/x86/entry/calling.h | 26 +++++++-
arch/x86/entry/entry_64.S | 22 +++++++
arch/x86/include/asm/asi.h | 122 ++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/asi_session.h | 7 ++
arch/x86/include/asm/mmu_context.h | 3 +-
arch/x86/kernel/asm-offsets.c | 5 ++
arch/x86/mm/asi.c | 67 +++++++++++++++++---
7 files changed, 242 insertions(+), 10 deletions(-)

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 0789e13..ca23b79 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -6,6 +6,7 @@
#include <asm/percpu.h>
#include <asm/asm-offsets.h>
#include <asm/processor-flags.h>
+#include <asm/asi.h>

/*

@@ -172,7 +173,30 @@
.endif
.endm

-#ifdef CONFIG_PAGE_TABLE_ISOLATION
+#if defined(CONFIG_ADDRESS_SPACE_ISOLATION)
+
+/*
+ * For now, ASI is not compatible with PTI.
+ */
+
+.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
+.endm
+
+.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req
+.endm
+
+.macro SWITCH_TO_USER_CR3_STACK scratch_reg:req
+.endm
+
+.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
+ ASI_INTERRUPT_AND_SAVE_CR3 \scratch_reg \save_reg
+.endm
+
+.macro RESTORE_CR3 scratch_reg:req save_reg:req
+ ASI_RESUME_AND_RESTORE_CR3 \save_reg
+.endm
+
+#elif defined(CONFIG_PAGE_TABLE_ISOLATION)

/*
* PAGE_TABLE_ISOLATION PGDs are 8k. Flip bit 12 to switch between the two
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 76942cb..fddb820 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -573,7 +573,15 @@ SYM_CODE_START(interrupt_entry)

CALL_enter_from_user_mode

+#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
+ jmp 2f
+#endif
1:
+#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
+ /* Interrupt address space isolation if it is active */
+ ASI_INTERRUPT scratch_reg=%rdi
+2:
+#endif
ENTER_IRQ_STACK old_rsp=%rdi save_ret=1
/* We entered an interrupt context - irqs are off: */
TRACE_IRQS_OFF
@@ -674,6 +682,10 @@ retint_kernel:
call preempt_schedule_irq
1:
#endif
+#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
+ ASI_PREPARE_RESUME
+ ASI_RESUME scratch_reg=%rdi
+#endif
/*
* The iretq could re-enable interrupts:
*/
@@ -1238,6 +1250,9 @@ SYM_CODE_START_LOCAL(paranoid_entry)
* This is also why CS (stashed in the "iret frame" by the
* hardware at entry) can not be used: this may be a return
* to kernel code, but with a user CR3 value.
+ *
+ * If ASI is enabled, this also handles the case where we are
+ * using an ASI CR3 value.
*/
SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14

@@ -1313,6 +1328,13 @@ SYM_CODE_START_LOCAL(error_entry)

.Lerror_entry_done_lfence:
FENCE_SWAPGS_KERNEL_ENTRY
+#ifdef CONFIG_ADDRESS_SPACE_ISOLATION
+ /*
+ * Interrupt address space isolation if it is active. This will restore
+ * the original kernel CR3.
+ */
+ ASI_INTERRUPT scratch_reg=%rdi
+#endif
.Lerror_entry_done:
ret

diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
index bcfb68e..d240954 100644
--- a/arch/x86/include/asm/asi.h
+++ b/arch/x86/include/asm/asi.h
@@ -108,6 +108,128 @@ struct asi {
extern int asi_enter(struct asi *asi);
extern void asi_exit(struct asi *asi);

+#else /* __ASSEMBLY__ */
+
+#include <asm/alternative-asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/cpufeatures.h>
+#include <asm/percpu.h>
+#include <asm/processor-flags.h>
+
+#define THIS_ASI_SESSION_asi \
+ PER_CPU_VAR(cpu_tlbstate + TLB_STATE_asi)
+#define THIS_ASI_SESSION_isolation_cr3 \
+ PER_CPU_VAR(cpu_tlbstate + TLB_STATE_asi_isolation_cr3)
+#define THIS_ASI_SESSION_original_cr3 \
+ PER_CPU_VAR(cpu_tlbstate + TLB_STATE_asi_original_cr3)
+#define THIS_ASI_SESSION_idepth \
+ PER_CPU_VAR(cpu_tlbstate + TLB_STATE_asi_idepth)
+
+.macro SET_NOFLUSH_BIT reg:req
+ bts $X86_CR3_PCID_NOFLUSH_BIT, \reg
+.endm
+
+/*
+ * Switch CR3 to the original kernel CR3 value. This is used when exiting
+ * interrupting ASI.
+ */
+.macro ASI_SWITCH_TO_KERNEL_CR3 scratch_reg:req
+ /*
+ * KERNEL pages can always resume with NOFLUSH as we do
+ * explicit flushes.
+ */
+ movq THIS_ASI_SESSION_original_cr3, \scratch_reg
+ ALTERNATIVE "", "SET_NOFLUSH_BIT \scratch_reg", X86_FEATURE_PCID
+ movq \scratch_reg, %cr3
+.endm
+
+/*
+ * Interrupt ASI, when there's an interrupt or exception while we
+ * were running with ASI.
+ */
+.macro ASI_INTERRUPT scratch_reg:req
+ movq THIS_ASI_SESSION_asi, \scratch_reg
+ testq \scratch_reg, \scratch_reg
+ jz .Lasi_interrupt_done_\@
+ incl THIS_ASI_SESSION_idepth
+ cmp $1, THIS_ASI_SESSION_idepth
+ jne .Lasi_interrupt_done_\@
+ ASI_SWITCH_TO_KERNEL_CR3 \scratch_reg
+.Lasi_interrupt_done_\@:
+.endm
+
+.macro ASI_PREPARE_RESUME
+ call asi_prepare_resume
+.endm
+
+/*
+ * Resume ASI, after it was interrupted by an interrupt or an exception.
+ */
+.macro ASI_RESUME scratch_reg:req
+ movq THIS_ASI_SESSION_asi, \scratch_reg
+ testq \scratch_reg, \scratch_reg
+ jz .Lasi_resume_done_\@
+ decl THIS_ASI_SESSION_idepth
+ jnz .Lasi_resume_done_\@
+ movq THIS_ASI_SESSION_isolation_cr3, \scratch_reg
+ mov \scratch_reg, %cr3
+.Lasi_resume_done_\@:
+.endm
+
+/*
+ * Interrupt ASI, special processing when ASI is interrupted by a NMI
+ * or a paranoid interrupt/exception.
+ */
+.macro ASI_INTERRUPT_AND_SAVE_CR3 scratch_reg:req save_reg:req
+ movq %cr3, \save_reg
+ /*
+ * Test the ASI PCID bits. If set, then an ASI page table
+ * is active. If clear, CR3 already has the kernel page table
+ * active.
+ */
+ bt $ASI_PGTABLE_BIT, \save_reg
+ jnc .Ldone_\@
+ incl THIS_ASI_SESSION_idepth
+ ASI_SWITCH_TO_KERNEL_CR3 \scratch_reg
+.Ldone_\@:
+.endm
+
+/*
+ * Resume ASI, special processing when ASI is resumed from a NMI
+ * or a paranoid interrupt/exception.
+ */
+.macro ASI_RESUME_AND_RESTORE_CR3 save_reg:req
+
+ ALTERNATIVE "jmp .Lwrite_cr3_\@", "", X86_FEATURE_PCID
+
+ bt $ASI_PGTABLE_BIT, \save_reg
+ jnc .Lrestore_kernel_cr3_\@
+
+ /*
+ * Restore ASI CR3. We need to update TLB flushing
+ * information.
+ */
+ movq THIS_ASI_SESSION_asi, %rdi
+ movq \save_reg, %rsi
+ call asi_update_flush
+ movq %rax, THIS_ASI_SESSION_isolation_cr3
+ decl THIS_ASI_SESSION_idepth
+ movq %rax, %cr3
+ jmp .Ldone_\@
+
+.Lrestore_kernel_cr3_\@:
+ /*
+ * Restore kernel CR3. KERNEL pages can always resume
+ * with NOFLUSH as we do explicit flushes.
+ */
+ SET_NOFLUSH_BIT \save_reg
+
+.Lwrite_cr3_\@:
+ movq \save_reg, %cr3
+
+.Ldone_\@:
+.endm
+
#endif /* __ASSEMBLY__ */

#endif /* CONFIG_ADDRESS_SPACE_ISOLATION */
diff --git a/arch/x86/include/asm/asi_session.h b/arch/x86/include/asm/asi_session.h
index 9d39c93..85968f7 100644
--- a/arch/x86/include/asm/asi_session.h
+++ b/arch/x86/include/asm/asi_session.h
@@ -10,6 +10,13 @@ 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 */
+ /*
+ * The interrupt depth (idepth) tracks interrupt (actually
+ * interrupt/exception/NMI) nesting. ASI is interrupted on
+ * the first interrupt, and it is resumed when that interrupt
+ * handler returns.
+ */
+ unsigned int idepth; /* interrupt depth */
};

#endif /* CONFIG_ADDRESS_SPACE_ISOLATION */
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 2d65443..b29e866 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -358,7 +358,8 @@ static inline unsigned long __get_current_cr3_fast(void)
* field of the ASI session.
*/
if (IS_ENABLED(CONFIG_ADDRESS_SPACE_ISOLATION) &&
- this_cpu_read(cpu_asi_session.asi)) {
+ this_cpu_read(cpu_asi_session.asi) &&
+ !this_cpu_read(cpu_asi_session.idepth)) {
cr3 = this_cpu_read(cpu_asi_session.isolation_cr3);
/* CR3 read never returns with the NOFLUSH bit */
cr3 &= ~X86_CR3_PCID_NOFLUSH;
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 5c7ee3d..a4316aa 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -95,6 +95,11 @@ static void __used common(void)

/* TLB state for the entry code */
OFFSET(TLB_STATE_user_pcid_flush_mask, tlb_state, user_pcid_flush_mask);
+ OFFSET(TLB_STATE_asi, tlb_state, asi_session.asi);
+ OFFSET(TLB_STATE_asi_isolation_cr3, tlb_state,
+ asi_session.isolation_cr3);
+ OFFSET(TLB_STATE_asi_original_cr3, tlb_state, asi_session.original_cr3);
+ OFFSET(TLB_STATE_asi_idepth, tlb_state, asi_session.idepth);

/* Layout info for cpu_entry_area */
OFFSET(CPU_ENTRY_AREA_entry_stack, cpu_entry_area, entry_stack_page);
diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
index cf0d122..c91ba82 100644
--- a/arch/x86/mm/asi.c
+++ b/arch/x86/mm/asi.c
@@ -68,7 +68,7 @@ void asi_set_pagetable(struct asi *asi, pgd_t *pagetable)
* Return an updated ASI CR3 value which specified if TLB needs to
* be flushed or not.
*/
-static unsigned long asi_update_flush(struct asi *asi, unsigned long asi_cr3)
+unsigned long asi_update_flush(struct asi *asi, unsigned long asi_cr3)
{
struct asi_tlb_pgtable *tlb_pgtable;
struct asi_tlb_state *tlb_state;
@@ -90,7 +90,24 @@ static unsigned long asi_update_flush(struct asi *asi, unsigned long asi_cr3)
return asi_cr3;
}

-static void asi_switch_to_asi_cr3(struct asi *asi)
+
+/*
+ * Switch to the ASI pagetable.
+ *
+ * If schedule is ASI_SWITCH_NOW, then immediately switch to the ASI
+ * pagetable by updating the CR3 register with the ASI CR3 value.
+ * Otherwise, if schedule is ASI_SWITCH_ON_RESUME, prepare everything
+ * for switching to ASI pagetable but do not update the CR3 register
+ * yet. This will be done by the next ASI_RESUME call.
+ */
+
+enum asi_switch_schedule {
+ ASI_SWITCH_NOW,
+ ASI_SWITCH_ON_RESUME,
+};
+
+static void asi_switch_to_asi_cr3(struct asi *asi,
+ enum asi_switch_schedule schedule)
{
unsigned long original_cr3, asi_cr3;
struct asi_session *asi_session;
@@ -114,8 +131,16 @@ static void asi_switch_to_asi_cr3(struct 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);
+ if (schedule == ASI_SWITCH_ON_RESUME) {
+ /*
+ * Defer the CR3 update the next ASI resume by setting
+ * the interrupt depth to 1.
+ */
+ asi_session->idepth = 1;
+ } else {
+ /* Update CR3 to immediately enter ASI */
+ native_write_cr3(asi_cr3);
+ }
}

static void asi_switch_to_kernel_cr3(struct asi *asi)
@@ -132,6 +157,7 @@ static void asi_switch_to_kernel_cr3(struct asi *asi)

asi_session = &get_cpu_var(cpu_asi_session);
asi_session->asi = NULL;
+ asi_session->idepth = 0;
}

int asi_enter(struct asi *asi)
@@ -153,7 +179,7 @@ int asi_enter(struct asi *asi)
}

local_irq_save(flags);
- asi_switch_to_asi_cr3(asi);
+ asi_switch_to_asi_cr3(asi, ASI_SWITCH_NOW);
local_irq_restore(flags);

return 0;
@@ -162,8 +188,10 @@ int asi_enter(struct asi *asi)

void asi_exit(struct asi *asi)
{
+ struct asi_session *asi_session;
struct asi *current_asi;
unsigned long flags;
+ int idepth;

current_asi = this_cpu_read(cpu_asi_session.asi);
if (!current_asi) {
@@ -173,8 +201,31 @@ void asi_exit(struct asi *asi)

WARN_ON(current_asi != asi);

- local_irq_save(flags);
- asi_switch_to_kernel_cr3(asi);
- local_irq_restore(flags);
+ idepth = this_cpu_read(cpu_asi_session.idepth);
+ if (!idepth) {
+ local_irq_save(flags);
+ asi_switch_to_kernel_cr3(asi);
+ local_irq_restore(flags);
+ } else {
+ /*
+ * ASI was interrupted so we already switched back
+ * to the back to the kernel page table and we just
+ * need to clear the ASI session.
+ */
+ asi_session = &get_cpu_var(cpu_asi_session);
+ asi_session->asi = NULL;
+ asi_session->idepth = 0;
+ }
}
EXPORT_SYMBOL(asi_exit);
+
+void asi_prepare_resume(void)
+{
+ struct asi_session *asi_session;
+
+ asi_session = &get_cpu_var(cpu_asi_session);
+ if (!asi_session->asi || asi_session->idepth > 1)
+ return;
+
+ asi_switch_to_asi_cr3(asi_session->asi, ASI_SWITCH_ON_RESUME);
+}
--
1.7.1
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