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

Borislav Petkov
2020-09-07T11:21:59Z

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@kernel.org>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> 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.