From: Rik van Riel <riel@surriel.com>
To: Hou Wenlong <houwenlong.hwl@antgroup.com>, linux-kernel@vger.kernel.org
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 1/3] x86/mm: Correct the actual count of available global ASIDs
Date: Sat, 29 Mar 2025 13:29:25 -0400 [thread overview]
Message-ID: <a84047c77c1a5f16b0d25f0cee6fe86487d14a5b.camel@surriel.com> (raw)
In-Reply-To: <0954cb7ec766d6d1e0b66a93876762b516ae9bae.1743250122.git.houwenlong.hwl@antgroup.com>
On Sat, 2025-03-29 at 21:05 +0800, Hou Wenlong wrote:
>
> +++ b/arch/x86/mm/tlb.c
> @@ -279,7 +279,7 @@ static DEFINE_RAW_SPINLOCK(global_asid_lock);
> static u16 last_global_asid = MAX_ASID_AVAILABLE;
> static DECLARE_BITMAP(global_asid_used, MAX_ASID_AVAILABLE);
> static DECLARE_BITMAP(global_asid_freed, MAX_ASID_AVAILABLE);
> -static int global_asid_available = MAX_ASID_AVAILABLE -
> TLB_NR_DYN_ASIDS - 1;
> +static int global_asid_available = MAX_ASID_AVAILABLE -
> TLB_NR_DYN_ASIDS;
Unfortunately we are limited by the PCID space.
A process with ASID N will get PCID N+1.
The PCID space has the same size (and maximum value)
as the ASID space.
That means we cannot use the top ASID value.
Alternatively, I suppose we could have ASID and PCID
line up, and always exclude ASID 0 from being used.
That might (maybe) be prettier code, but it isn't what
we have today.
--
All Rights Reversed.
next prev parent reply other threads:[~2025-03-29 17:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-29 13:05 [PATCH 0/3] Fix some ASID range size calculation issues in global ASID allocation Hou Wenlong
2025-03-29 13:05 ` [PATCH 1/3] x86/mm: Correct the actual count of available global ASIDs Hou Wenlong
2025-03-29 17:29 ` Rik van Riel [this message]
2025-03-31 3:46 ` Hou Wenlong
2025-03-29 13:05 ` [PATCH 2/3] mm/tlb: Fix wrong judgement in allocate_global_asid() Hou Wenlong
2025-03-29 17:33 ` Rik van Riel
2025-03-31 5:12 ` Hou Wenlong
2025-03-31 12:58 ` Hou Wenlong
2025-03-29 13:05 ` [PATCH 3/3] x86/mm: Fix wrong usage of 'MAX_ASID_AVAILABLE' in global ASID allocation Hou Wenlong
2025-03-30 1:11 ` Rik van Riel
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