From: "tip-bot2 for Balbir Singh" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>,
Balbir Singh <sblbir@amazon.com>, x86 <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/pti] x86/mm: Refactor cond_ibpb() to support other use cases
Date: Wed, 16 Sep 2020 13:11:19 -0000 [thread overview]
Message-ID: <160026187981.15536.17927491932304015051.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200510014803.12190-4-sblbir@amazon.com>
The following commit has been merged into the x86/pti branch of tip:
Commit-ID: 81f449985c12b83b91849d94724b803ebf856301
Gitweb: https://git.kernel.org/tip/81f449985c12b83b91849d94724b803ebf856301
Author: Balbir Singh <sblbir@amazon.com>
AuthorDate: Wed, 29 Jul 2020 10:11:00 +10:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 16 Sep 2020 15:08:02 +02:00
x86/mm: Refactor cond_ibpb() to support other use cases
cond_ibpb() has the necessary bits required to track the previous mm in
switch_mm_irqs_off(). This can be reused for other use cases like L1D
flushing on context switch.
[ tglx: Moved comment, added a separate define for state (re)initialization ]
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Balbir Singh <sblbir@amazon.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200510014803.12190-4-sblbir@amazon.com
Link: https://lore.kernel.org/r/20200729001103.6450-3-sblbir@amazon.com
---
arch/x86/include/asm/tlbflush.h | 2 +-
arch/x86/mm/tlb.c | 53 +++++++++++++++++---------------
2 files changed, 30 insertions(+), 25 deletions(-)
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 8c87a2e..a927d40 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -83,7 +83,7 @@ struct tlb_state {
/* Last user mm for optimizing IBPB */
union {
struct mm_struct *last_user_mm;
- unsigned long last_user_mm_ibpb;
+ unsigned long last_user_mm_spec;
};
u16 loaded_mm_asid;
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 0951b47..6bbd758 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -43,10 +43,14 @@
*/
/*
- * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer which is
- * stored in cpu_tlb_state.last_user_mm_ibpb.
+ * Bits to mangle the TIF_SPEC_IB state into the mm pointer which is
+ * stored in cpu_tlb_state.last_user_mm_spec.
*/
#define LAST_USER_MM_IBPB 0x1UL
+#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB)
+
+/* Bits to set when tlbstate and flush is (re)initialized */
+#define LAST_USER_MM_INIT LAST_USER_MM_IBPB
/*
* The x86 feature is called PCID (Process Context IDentifier). It is similar
@@ -317,20 +321,29 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
local_irq_restore(flags);
}
-static inline unsigned long mm_mangle_tif_spec_ib(struct task_struct *next)
+static inline unsigned long mm_mangle_tif_spec_bits(struct task_struct *next)
{
unsigned long next_tif = task_thread_info(next)->flags;
- unsigned long ibpb = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_IBPB;
+ unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK;
- return (unsigned long)next->mm | ibpb;
+ return (unsigned long)next->mm | spec_bits;
}
-static void cond_ibpb(struct task_struct *next)
+static void cond_mitigation(struct task_struct *next)
{
+ unsigned long prev_mm, next_mm;
+
if (!next || !next->mm)
return;
+ next_mm = mm_mangle_tif_spec_bits(next);
+ prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_spec);
+
/*
+ * Avoid user/user BTB poisoning by flushing the branch predictor
+ * when switching between processes. This stops one process from
+ * doing Spectre-v2 attacks on another.
+ *
* Both, the conditional and the always IBPB mode use the mm
* pointer to avoid the IBPB when switching between tasks of the
* same process. Using the mm pointer instead of mm->context.ctx_id
@@ -340,8 +353,6 @@ static void cond_ibpb(struct task_struct *next)
* exposed data is not really interesting.
*/
if (static_branch_likely(&switch_mm_cond_ibpb)) {
- unsigned long prev_mm, next_mm;
-
/*
* This is a bit more complex than the always mode because
* it has to handle two cases:
@@ -371,20 +382,14 @@ static void cond_ibpb(struct task_struct *next)
* Optimize this with reasonably small overhead for the
* above cases. Mangle the TIF_SPEC_IB bit into the mm
* pointer of the incoming task which is stored in
- * cpu_tlbstate.last_user_mm_ibpb for comparison.
- */
- next_mm = mm_mangle_tif_spec_ib(next);
- prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_ibpb);
-
- /*
+ * cpu_tlbstate.last_user_mm_spec for comparison.
+ *
* Issue IBPB only if the mm's are different and one or
* both have the IBPB bit set.
*/
if (next_mm != prev_mm &&
(next_mm | prev_mm) & LAST_USER_MM_IBPB)
indirect_branch_prediction_barrier();
-
- this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, next_mm);
}
if (static_branch_unlikely(&switch_mm_always_ibpb)) {
@@ -393,11 +398,12 @@ static void cond_ibpb(struct task_struct *next)
* different context than the user space task which ran
* last on this CPU.
*/
- if (this_cpu_read(cpu_tlbstate.last_user_mm) != next->mm) {
+ if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) !=
+ (unsigned long)next->mm)
indirect_branch_prediction_barrier();
- this_cpu_write(cpu_tlbstate.last_user_mm, next->mm);
- }
}
+
+ this_cpu_write(cpu_tlbstate.last_user_mm_spec, next_mm);
}
#ifdef CONFIG_PERF_EVENTS
@@ -519,11 +525,10 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
need_flush = true;
} else {
/*
- * Avoid user/user BTB poisoning by flushing the branch
- * predictor when switching between processes. This stops
- * one process from doing Spectre-v2 attacks on another.
+ * Apply process to process speculation vulnerability
+ * mitigations if applicable.
*/
- cond_ibpb(tsk);
+ cond_mitigation(tsk);
/*
* Stop remote flushes for the previous mm.
@@ -631,7 +636,7 @@ void initialize_tlbstate_and_flush(void)
write_cr3(build_cr3(mm->pgd, 0));
/* Reinitialize tlbstate. */
- this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, LAST_USER_MM_IBPB);
+ this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_INIT);
this_cpu_write(cpu_tlbstate.loaded_mm_asid, 0);
this_cpu_write(cpu_tlbstate.next_asid, 1);
this_cpu_write(cpu_tlbstate.ctxs[0].ctx_id, mm->context.ctx_id);
next prev parent reply other threads:[~2020-09-16 20:27 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-10 1:47 [PATCH v6 0/6] Optionally flush L1D on context switch Balbir Singh
2020-05-10 1:47 ` [PATCH v6 1/6] arch/x86/kvm: Refactor l1d flush lifecycle management Balbir Singh
2020-05-13 13:35 ` Thomas Gleixner
2020-05-14 8:23 ` Singh, Balbir
2020-05-13 13:53 ` Thomas Gleixner
2020-05-14 8:25 ` Singh, Balbir
2020-05-22 9:32 ` [tip: x86/mm] x86/kvm: Refactor L1D flush page management tip-bot2 for Balbir Singh
2020-05-10 1:47 ` [PATCH v6 2/6] arch/x86/kvm: Refactor tlbflush and l1d flush Balbir Singh
2020-05-22 9:32 ` [tip: x86/mm] x86/kvm: Refactor L1D flush operations tip-bot2 for Balbir Singh
2020-05-10 1:48 ` [PATCH v6 3/6] arch/x86/mm: Refactor cond_ibpb() to support other use cases Balbir Singh
2020-05-13 14:16 ` Thomas Gleixner
2020-05-22 9:32 ` [tip: x86/mm] x86/mm: " tip-bot2 for Balbir Singh
2020-09-16 13:11 ` tip-bot2 for Balbir Singh [this message]
2020-05-10 1:48 ` [PATCH v6 4/6] arch/x86/kvm: Refactor L1D flushing Balbir Singh
2020-05-22 9:32 ` [tip: x86/mm] x86/kvm: " tip-bot2 for Balbir Singh
2020-05-10 1:48 ` [PATCH v6 5/6] Optionally flush L1D on context switch Balbir Singh
2020-05-13 15:04 ` Thomas Gleixner
2020-05-14 8:23 ` Singh, Balbir
2020-05-13 15:27 ` Thomas Gleixner
2020-05-14 21:28 ` Singh, Balbir
2020-05-13 16:16 ` Thomas Gleixner
2020-05-14 7:43 ` Singh, Balbir
2020-05-14 11:33 ` Thomas Gleixner
2020-05-10 1:48 ` [PATCH v6 6/6] Documentation: Add L1D flushing Documentation Balbir Singh
2020-05-13 13:33 ` Thomas Gleixner
2020-05-14 1:12 ` Singh, Balbir
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=160026187981.15536.17927491932304015051.tip-bot2@tip-bot2 \
--to=tip-bot2@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=sblbir@amazon.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).