Re: [PATCH v7 9/9] x86/mmu: Allocate/free PASID

[Borislav Petkov]

On Thu, Aug 27, 2020 at 08:06:34AM -0700, Fenghua Yu wrote:
> A PASID is allocated for an "mm" the first time any thread binds
> to an SVM capable device and is freed from the "mm" when the SVM is
> unbound by the last thread. It's possible for the "mm" to have different
> PASID values in different binding/unbinding SVM cycles.
> 
> The mm's PASID (non-zero for valid PASID or 0 for invalid PASID) is
> propagated to per-thread PASID MSR for all threads within the mm through
> through IPI, context switch, or inherit to ensure a running thread has
> the right PASID MSR matching the mm's PASID.

That sentence has grown too large and confused. Pls fix.

> Suggested-by: Andy Lutomirski <luto@xxxxxxxxxx>
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> v7:
> - Don't fix up PASID in #GP. Instead, update the PASID MSR by IPI and
>   context switch after PASID allocation and free. Inherit PASID from
>   parent. (Andy)
> 
> Before v7:
> - Allocate a PASID for the mm and free it until mm exit.
> 
>  arch/x86/include/asm/disabled-features.h |  2 +-
>  arch/x86/include/asm/fpu/api.h           | 12 +++++
>  arch/x86/include/asm/fpu/internal.h      |  2 +
>  arch/x86/kernel/fpu/xstate.c             | 56 ++++++++++++++++++++++++
>  drivers/iommu/intel/svm.c                | 28 +++++++++++-
>  5 files changed, 98 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index 588d83e9da49..5861d34f9771 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -56,7 +56,7 @@
>  # define DISABLE_PTI		(1 << (X86_FEATURE_PTI & 31))
>  #endif
>  
> -#ifdef CONFIG_INTEL_IOMMU_SVM
> +#ifdef CONFIG_IOMMU_SUPPORT
>  # define DISABLE_ENQCMD	0
>  #else
>  # define DISABLE_ENQCMD (1 << (X86_FEATURE_ENQCMD & 31))

That hunk belongs with the previous patch.

> diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
> index b774c52e5411..dcd9503b1098 100644
> --- a/arch/x86/include/asm/fpu/api.h
> +++ b/arch/x86/include/asm/fpu/api.h
> @@ -62,4 +62,16 @@ extern void switch_fpu_return(void);
>   */
>  extern int cpu_has_xfeatures(u64 xfeatures_mask, const char **feature_name);
>  
> +/*
> + * Tasks that are not using SVA have mm->pasid set to zero to note that they
> + * will not have the valid bit set in MSR_IA32_PASID while they are running.
> + */
> +#define PASID_DISABLED	0
> +
> +#ifdef CONFIG_IOMMU_SUPPORT
> +/* Update current's PASID MSR/state by mm's PASID. */
> +void update_pasid(void);
> +#else
> +static inline void update_pasid(void) { }
> +#endif
>  #endif /* _ASM_X86_FPU_API_H */
> diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
> index 0a460f2a3f90..2d737e02b59a 100644
> --- a/arch/x86/include/asm/fpu/internal.h
> +++ b/arch/x86/include/asm/fpu/internal.h
> @@ -583,6 +583,8 @@ static inline void switch_fpu_finish(struct fpu *new_fpu)
>  			pkru_val = pk->pkru;
>  	}
>  	__write_pkru(pkru_val);
> +
> +	update_pasid();
>  }
>  
>  /*
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 67f1a03b9b23..556040e14f1c 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -1402,3 +1402,59 @@ int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
>  	return 0;
>  }
>  #endif /* CONFIG_PROC_PID_ARCH_STATUS */
> +
> +#ifdef CONFIG_IOMMU_SUPPORT
> +void update_pasid(void)
> +{
> +	u64 pasid_state;
> +	u32 pasid;
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> +		return;
> +
> +	if (!current->mm)
> +		return;
> +
> +	pasid = READ_ONCE(current->mm->pasid);
> +	/* Set the valid bit in the PASID MSR/state only for valid pasid. */
> +	pasid_state = pasid == PASID_DISABLED ?
> +		      pasid : pasid | MSR_IA32_PASID_VALID;
> +
> +	/*
> +	 * No need to hold fregs_lock() since the task's fpstate won't
> +	 * be changed by others (e.g. ptrace) while the task is being
> +	 * switched to or is in IPI.
> +	 */
> +	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
> +		/* The MSR is active and can be directly updated. */
> +		wrmsrl(MSR_IA32_PASID, pasid_state);
> +	} else {
> +		struct fpu *fpu = &current->thread.fpu;
> +		struct ia32_pasid_state *ppasid_state;
> +		struct xregs_state *xsave;
> +
> +		/*
> +		 * The CPU's xstate registers are not currently active. Just
> +		 * update the PASID state in the memory buffer here. The
> +		 * PASID MSR will be loaded when returning to user mode.
> +		 */
> +		xsave = &fpu->state.xsave;
> +		xsave->header.xfeatures |= XFEATURE_MASK_PASID;
> +		ppasid_state = get_xsave_addr(xsave, XFEATURE_PASID);
> +		if (ppasid_state) {
> +			/*
> +			 * Only update the task's PASID state when it's
> +			 * different from the mm's pasid.
> +			 */
> +			if (ppasid_state->pasid != pasid_state) {
> +				/*
> +				 * Invalid fpregs so that xrstors will pick up
							  ^^^^^^^

Not "xrstors" but the "state restoring" or so.


> +				 * the PASID state.
> +				 */
> +				__fpu_invalidate_fpregs_state(fpu);
> +				ppasid_state->pasid = pasid_state;
> +			}

What happens if get_xsave_addr() returns NULL? A WARN_ONCE maybe?

Ok, done with review.

Thx.

-- 
Regards/Gruss,
    Boris.

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