Re: [PATCH v14 07/13] x86/mm: add global ASID allocation helper functions

[Borislav Petkov]

On Tue, Feb 25, 2025 at 10:00:42PM -0500, Rik van Riel wrote:
> Add functions to manage global ASID space. Multithreaded processes that
> are simultaneously active on 4 or more CPUs can get a global ASID,
> resulting in the same PCID being used for that process on every CPU.
> 
> This in turn will allow the kernel to use hardware-assisted TLB flushing
> through AMD INVLPGB or Intel RAR for these processes.
> 
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
> Tested-by: Manali Shukla <Manali.Shukla@xxxxxxx>
> Tested-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
> Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> ---
>  arch/x86/include/asm/mmu.h         |  11 +++
>  arch/x86/include/asm/mmu_context.h |   2 +
>  arch/x86/include/asm/tlbflush.h    |  43 +++++++++
>  arch/x86/mm/tlb.c                  | 146 ++++++++++++++++++++++++++++-
>  4 files changed, 199 insertions(+), 3 deletions(-)

Some small touchups ontop:

--- /tmp/current.patch	2025-03-02 07:33:13.913105249 +0100
+++ /tmp/0001-x86-mm-Add-global-ASID-allocation-helper-functions.patch	2025-03-02 08:05:23.613262232 +0100
 diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
-index 3b496cdcb74b..edb5942d4829 100644
+index 3b496cdcb74b..7fbefea5fdae 100644
 --- a/arch/x86/include/asm/mmu.h
 +++ b/arch/x86/include/asm/mmu.h
@@ -35,6 +38,7 @@ index 3b496cdcb74b..edb5942d4829 100644
 +	 * hardware-assisted remote TLB invalidation like AMD INVLPGB.
 +	 */
 +	u16 global_asid;
++
 +	/* The process is transitioning to a new global ASID number. */
 +	bool asid_transition;
 +#endif
@@ -251,7 +255,12 @@ index 1cc25e83bd34..9b1652c02452 100644
 +	if (mm_global_asid(mm))
 +		return;
 +
-+	/* The last global ASID was consumed while waiting for the lock. */
++	/*
++	 * The last global ASID was consumed while waiting for the lock.
++	 *
++	 * If this fires, a more aggressive ASID reuse scheme might be
++	 * needed.
++	 */
 +	if (!global_asid_available) {
 +		VM_WARN_ONCE(1, "Ran out of global ASIDs\n");
 +		return;
@@ -284,5 +293,5 @@ index 1cc25e83bd34..9b1652c02452 100644
   * Given an ASID, flush the corresponding user ASID.  We can delay this
   * until the next time we switch to it.
 -- 

-- 
Regards/Gruss,
    Boris.

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