linux-kernel - Re: [PATCHv3 4/8] x86/mm: Handle LAM on context switch

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Date:   Thu, 16 Jun 2022 19:40:12 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, namit@...are.com
Subject: Re: [PATCHv3 4/8] x86/mm: Handle LAM on context switch

On Thu, Jun 16, 2022 at 11:08:07AM +0200, Peter Zijlstra wrote:
> Either use that one spare byte, or find room elsewhere I suppose.

Okay, I will put into the byte after invalidate_other and modify
tlbstate_lam_cr3_mask() and set_tlbstate_lam_cr3_mask() to shift it
accordingly.

It looks like this:

struct tlb_state {
	struct mm_struct *         loaded_mm;            /*     0     8 */
	union {
		struct mm_struct * last_user_mm;         /*     8     8 */
		unsigned long      last_user_mm_spec;    /*     8     8 */
	};                                               /*     8     8 */
	union {
		struct mm_struct *         last_user_mm;         /*     0     8 */
		unsigned long              last_user_mm_spec;    /*     0     8 */
	};

	u16                        loaded_mm_asid;       /*    16     2 */
	u16                        next_asid;            /*    18     2 */
	bool                       invalidate_other;     /*    20     1 */
	u8                         lam;                  /*    21     1 */
	unsigned short             user_pcid_flush_mask; /*    22     2 */
	unsigned long              cr4;                  /*    24     8 */
	struct tlb_context         ctxs[6];              /*    32    96 */

	/* size: 128, cachelines: 2, members: 9 */
};

-- 
 Kirill A. Shutemov