linux-kernel - Re: [PATCH 5/8] x86/mmu: Add mm-based PASID refcounting

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Message-ID: <874ka387tj.ffs@tglx>
Date:   Wed, 29 Sep 2021 22:07:04 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck, Tony" <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Jacob Jun Pan <jacob.jun.pan@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        iommu@...ts.linux-foundation.org,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] x86/mmu: Add mm-based PASID refcounting

On Wed, Sep 29 2021 at 11:31, Tony Luck wrote:
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index a58800973aed..5a3c87fd65de 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -528,6 +528,32 @@ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs,
>  
>  #define GPFSTR "general protection fault"
>  
> +/*
> + * When a user executes the ENQCMD instruction it will #GP
> + * fault if the IA32_PASID MSR has not been set up with a
> + * valid PASID.
> + * So if the process has been allocated a PASID (mm->pasid)
> + * AND the IA32_PASID MSR has not been initialized, try to
> + * fix this #GP by initializing the IA32_PASID MSR.
> + * If the #GP was for some other reason, it will trigger
> + * again, but this routine will return false and the #GP
> + * will be processed.
> + */
> +static void try_fixup_pasid(void)
> +{
> +	if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> +		return false;
> +
> +#ifdef CONFIG_IOMMU_SUPPORT
> +	if (current->mm->pasid && !current->pasid_activated) {
> +		current->pasid_activated = 1;
> +		wrmsrl(MSR_IA32_PASID, current->mm->pasid);
> +		return true;
> +	}
> +#endif
> +	return false;
> +}
> +
>  DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
>  {
>  	char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
> @@ -536,6 +562,9 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
>  	unsigned long gp_addr;
>  	int ret;
>  
> +	if (user_mode(regs) && try_fixup_pasid())
> +		return;
> +
>  	cond_local_irq_enable(regs);
>  
>  	if (static_cpu_has(X86_FEATURE_UMIP)) {

Amen.