linux-kernel - Re: [RFC PATCH 00/10] AMD broadcast TLB invalidation

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Message-ID: <20241222100621.258ea35c@fangorn>
Date: Sun, 22 Dec 2024 10:06:21 -0500
From: Rik van Riel <riel@...riel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
 dave.hansen@...ux.intel.com, luto@...nel.org, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, hpa@...or.com, akpm@...ux-foundation.org
Subject: Re: [RFC PATCH 00/10] AMD broadcast TLB invalidation

On Sun, 22 Dec 2024 12:11:13 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Sat, Dec 21, 2024 at 11:06:32PM -0500, Rik van Riel wrote:
> > Add support for broadcast TLB invalidation using AMD's INVLPGB instruction.
> > 
> > This allows the kernel to invalidate TLB entries on remote CPUs without
> > needing to send IPIs, without having to wait for remote CPUs to handle
> > those interrupts, and with less interruption to what was running on
> > those CPUs.  
> 
> You're going to be needing this somewhere at the start of this series.

I like this change, and would be happy to add it.

What exactly is it needed for?

When I add this change, what other things do
I need to be looking for?

Can we just set the function pointer to
tlb_remove_table, and get rid of the function,
like this?

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9d7bd0ae48c4..e8743f8c9fd0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -274,7 +274,7 @@ 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
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index fec381533555..2b78a6b466ed 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -59,11 +59,6 @@ void __init native_pv_lock_init(void)
 		static_branch_enable(&virt_spin_lock_key);
 }
 
-static void native_tlb_remove_table(struct mmu_gather *tlb, void *table)
-{
-	tlb_remove_page(tlb, table);
-}
-
 struct static_key paravirt_steal_enabled;
 struct static_key paravirt_steal_rq_enabled;
 
@@ -191,7 +186,7 @@ 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,