linux-kernel - Re: [PATCHv6 04/11] x86/mm: Handle LAM on context switch

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Date:   Mon, 15 Aug 2022 15:42:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
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>,
        Taras Madan <tarasmadan@...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
Subject: Re: [PATCHv6 04/11] x86/mm: Handle LAM on context switch

On Mon, Aug 15, 2022 at 07:17:56AM +0300, Kirill A. Shutemov wrote:
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index c1e31e9a85d7..fdc0b69b5da7 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c
> @@ -154,17 +154,18 @@ static inline u16 user_pcid(u16 asid)
>  	return ret;
>  }
>  
> -static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
> +static inline unsigned long build_cr3(pgd_t *pgd, u16 asid, unsigned long lam)
>  {
>  	if (static_cpu_has(X86_FEATURE_PCID)) {
> -		return __sme_pa(pgd) | kern_pcid(asid);
> +		return __sme_pa(pgd) | kern_pcid(asid) | lam;
>  	} else {
>  		VM_WARN_ON_ONCE(asid != 0);
> -		return __sme_pa(pgd);
> +		return __sme_pa(pgd) | lam;
>  	}
>  }
>  
> -static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
> +static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid,
> +					      unsigned long lam)
>  {
>  	VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
>  	/*
> @@ -173,7 +174,7 @@ static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
>  	 * boot because all CPU's the have same capabilities:
>  	 */
>  	VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID));
> -	return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
> +	return __sme_pa(pgd) | kern_pcid(asid) | lam | CR3_NOFLUSH;
>  }

Looking at this; I wonder if we want something like this:

--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -157,6 +157,7 @@ static inline u16 user_pcid(u16 asid)
 static inline unsigned long build_cr3(pgd_t *pgd, u16 asid, unsigned long lam)
 {
 	if (static_cpu_has(X86_FEATURE_PCID)) {
+		VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
 		return __sme_pa(pgd) | kern_pcid(asid) | lam;
 	} else {
 		VM_WARN_ON_ONCE(asid != 0);
@@ -167,14 +168,13 @@ static inline unsigned long build_cr3(pg
 static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid,
 					      unsigned long lam)
 {
-	VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
 	/*
 	 * Use boot_cpu_has() instead of this_cpu_has() as this function
 	 * might be called during early boot. This should work even after
 	 * boot because all CPU's the have same capabilities:
 	 */
 	VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID));
-	return __sme_pa(pgd) | kern_pcid(asid) | lam | CR3_NOFLUSH;
+	return build_cr3(pgd, asid, lam) | CR3_NOFLUSH;
 }
 
 /*