linux-kernel - [PATCH RFC v2 07/29] mm: asi: Make __get_current_cr3

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Message-ID: <20250110-asi-rfc-v2-v2-7-8419288bc805@google.com>
Date: Fri, 10 Jan 2025 18:40:33 +0000
From: Brendan Jackman <jackmanb@...gle.com>
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	Brendan Jackman <jackmanb@...gle.com>, Junaid Shahid <junaids@...gle.com>
Subject: [PATCH RFC v2 07/29] mm: asi: Make __get_current_cr3_fast() ASI-aware

From: Junaid Shahid <junaids@...gle.com>

When ASI is active, __get_current_cr3_fast() adjusts the returned CR3
value accordingly to reflect the actual ASI CR3.

Signed-off-by: Junaid Shahid <junaids@...gle.com>
Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 arch/x86/mm/tlb.c | 37 +++++++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 2601beed83aef182d88800c09d70e4c5e95e7ed0..b2a13fdab0c6454c1d9d4e3338801f3402da4191 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -20,6 +20,7 @@
 #include <asm/cache.h>
 #include <asm/cacheflush.h>
 #include <asm/apic.h>
+#include <asm/asi.h>
 #include <asm/perf_event.h>
 
 #include "mm_internal.h"
@@ -197,8 +198,8 @@ static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid,
 	return build_cr3(pgd, asid, lam) | CR3_NOFLUSH;
 }
 
-noinstr unsigned long build_cr3_pcid_noinstr(pgd_t *pgd, u16 pcid,
-					     unsigned long lam, bool noflush)
+static __always_inline unsigned long build_cr3_pcid(pgd_t *pgd, u16 pcid,
+						    unsigned long lam, bool noflush)
 {
 	u64 noflush_bit = 0;
 
@@ -210,6 +211,12 @@ noinstr unsigned long build_cr3_pcid_noinstr(pgd_t *pgd, u16 pcid,
 	return __build_cr3(pgd, pcid, lam) | noflush_bit;
 }
 
+noinstr unsigned long build_cr3_pcid_noinstr(pgd_t *pgd, u16 pcid,
+					     unsigned long lam, bool noflush)
+{
+	return build_cr3_pcid(pgd, pcid, lam, noflush);
+}
+
 /*
  * We get here when we do something requiring a TLB invalidation
  * but could not go invalidate all of the contexts.  We do the
@@ -1133,14 +1140,32 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
  */
 noinstr 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),
-			  tlbstate_lam_cr3_mask());
+	unsigned long cr3;
+	pgd_t *pgd;
+	u16 asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
+	struct asi *asi = asi_get_current();
+	u16 pcid;
+
+	if (asi) {
+		pgd = asi_pgd(asi);
+		pcid = asi_pcid(asi, asid);
+	} else {
+		pgd = this_cpu_read(cpu_tlbstate.loaded_mm)->pgd;
+		pcid = kern_pcid(asid);
+	}
+
+	cr3 = build_cr3_pcid(pgd, pcid, tlbstate_lam_cr3_mask(), false);
 
 	/* For now, be very restrictive about when this can be called. */
 	VM_WARN_ON(in_nmi() || preemptible());
 
+	/*
+	 * Outside of the ASI critical section, an ASI-restricted CR3 is
+	 * unstable because an interrupt (including an inner interrupt, if we're
+	 * already in one) could cause a persistent asi_exit.
+	 */
+	VM_WARN_ON_ONCE(asi && asi_in_critical_section());
+
 	VM_BUG_ON(cr3 != __read_cr3());
 	return cr3;
 }

-- 
2.47.1.613.gc27f4b7a9f-goog