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Message-ID: <59971fe5-31ec-defb-ead6-3e733aa371f7@linux.intel.com>
Date: Sat, 13 Jun 2020 21:07:24 +0800
From: Lu Baolu <baolu.lu@...ux.intel.com>
To: Fenghua Yu <fenghua.yu@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
H Peter Anvin <hpa@...or.com>,
David Woodhouse <dwmw2@...radead.org>,
Frederic Barrat <fbarrat@...ux.ibm.com>,
Andrew Donnellan <ajd@...ux.ibm.com>,
Felix Kuehling <Felix.Kuehling@....com>,
Joerg Roedel <joro@...tes.org>,
Dave Hansen <dave.hansen@...el.com>,
Tony Luck <tony.luck@...el.com>,
Ashok Raj <ashok.raj@...el.com>,
Jacob Jun Pan <jacob.jun.pan@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
Yu-cheng Yu <yu-cheng.yu@...el.com>,
Sohil Mehta <sohil.mehta@...el.com>,
Ravi V Shankar <ravi.v.shankar@...el.com>
Cc: baolu.lu@...ux.intel.com,
linux-kernel <linux-kernel@...r.kernel.org>,
x86 <x86@...nel.org>, iommu@...ts.linux-foundation.org,
amd-gfx <amd-gfx@...ts.freedesktop.org>,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 11/12] x86/mmu: Allocate/free PASID
Hi Fenghua,
On 2020/6/13 8:41, Fenghua Yu wrote:
> A PASID is allocated for an "mm" the first time any thread attaches
> to an SVM capable device. Later device attachments (whether to the same
> device or another SVM device) will re-use the same PASID.
>
> The PASID is freed when the process exits (so no need to keep
> reference counts on how many SVM devices are sharing the PASID).
FYI.
Jean-Philippe Brucker has a patch for mm->pasid management in the vendor
agnostic manner.
https://www.spinics.net/lists/iommu/msg44459.html
Best regards,
baolu
>
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
> v2:
> - Define a helper free_bind() to simplify error exit code in bind_mm()
> (Thomas)
> - Fix a ret error code in bind_mm() (Thomas)
> - Change pasid's type from "int" to "unsigned int" to have consistent
> pasid type in iommu (Thomas)
> - Simplify alloc_pasid() a bit.
>
> arch/x86/include/asm/iommu.h | 2 +
> arch/x86/include/asm/mmu_context.h | 14 ++++
> drivers/iommu/intel/svm.c | 101 +++++++++++++++++++++++++----
> 3 files changed, 105 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/include/asm/iommu.h b/arch/x86/include/asm/iommu.h
> index bf1ed2ddc74b..ed41259fe7ac 100644
> --- a/arch/x86/include/asm/iommu.h
> +++ b/arch/x86/include/asm/iommu.h
> @@ -26,4 +26,6 @@ arch_rmrr_sanity_check(struct acpi_dmar_reserved_memory *rmrr)
> return -EINVAL;
> }
>
> +void __free_pasid(struct mm_struct *mm);
> +
> #endif /* _ASM_X86_IOMMU_H */
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 47562147e70b..f8c91ce8c451 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -13,6 +13,7 @@
> #include <asm/tlbflush.h>
> #include <asm/paravirt.h>
> #include <asm/debugreg.h>
> +#include <asm/iommu.h>
>
> extern atomic64_t last_mm_ctx_id;
>
> @@ -117,9 +118,22 @@ static inline int init_new_context(struct task_struct *tsk,
> init_new_context_ldt(mm);
> return 0;
> }
> +
> +static inline void free_pasid(struct mm_struct *mm)
> +{
> + if (!IS_ENABLED(CONFIG_INTEL_IOMMU_SVM))
> + return;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
> + return;
> +
> + __free_pasid(mm);
> +}
> +
> static inline void destroy_context(struct mm_struct *mm)
> {
> destroy_context_ldt(mm);
> + free_pasid(mm);
> }
>
> extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index 4e775e12ae52..27dc866b8461 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -425,6 +425,53 @@ int intel_svm_unbind_gpasid(struct device *dev, unsigned int pasid)
> return ret;
> }
>
> +static void free_bind(struct intel_svm *svm, struct intel_svm_dev *sdev,
> + bool new_pasid)
> +{
> + if (new_pasid)
> + ioasid_free(svm->pasid);
> + kfree(svm);
> + kfree(sdev);
> +}
> +
> +/*
> + * If this mm already has a PASID, use it. Otherwise allocate a new one.
> + * Let the caller know if a new PASID is allocated via 'new_pasid'.
> + */
> +static int alloc_pasid(struct intel_svm *svm, struct mm_struct *mm,
> + unsigned int pasid_max, bool *new_pasid,
> + unsigned int flags)
> +{
> + unsigned int pasid;
> +
> + *new_pasid = false;
> +
> + /*
> + * Reuse the PASID if the mm already has a PASID and not a private
> + * PASID is requested.
> + */
> + if (mm && mm->pasid && !(flags & SVM_FLAG_PRIVATE_PASID)) {
> + /*
> + * Once a PASID is allocated for this mm, the PASID
> + * stays with the mm until the mm is dropped. Reuse
> + * the PASID which has been already allocated for the
> + * mm instead of allocating a new one.
> + */
> + ioasid_set_data(mm->pasid, svm);
> +
> + return mm->pasid;
> + }
> +
> + /* Allocate a new pasid. Do not use PASID 0, reserved for init PASID. */
> + pasid = ioasid_alloc(NULL, PASID_MIN, pasid_max - 1, svm);
> + if (pasid != INVALID_IOASID) {
> + /* A new pasid is allocated. */
> + *new_pasid = true;
> + }
> +
> + return pasid;
> +}
> +
> /* Caller must hold pasid_mutex, mm reference */
> static int
> intel_svm_bind_mm(struct device *dev, unsigned int flags,
> @@ -518,6 +565,8 @@ intel_svm_bind_mm(struct device *dev, unsigned int flags,
> init_rcu_head(&sdev->rcu);
>
> if (!svm) {
> + bool new_pasid;
> +
> svm = kzalloc(sizeof(*svm), GFP_KERNEL);
> if (!svm) {
> ret = -ENOMEM;
> @@ -529,12 +578,9 @@ intel_svm_bind_mm(struct device *dev, unsigned int flags,
> if (pasid_max > intel_pasid_max_id)
> pasid_max = intel_pasid_max_id;
>
> - /* Do not use PASID 0, reserved for RID to PASID */
> - svm->pasid = ioasid_alloc(NULL, PASID_MIN,
> - pasid_max - 1, svm);
> + svm->pasid = alloc_pasid(svm, mm, pasid_max, &new_pasid, flags);
> if (svm->pasid == INVALID_IOASID) {
> - kfree(svm);
> - kfree(sdev);
> + free_bind(svm, sdev, new_pasid);
> ret = -ENOSPC;
> goto out;
> }
> @@ -547,9 +593,7 @@ intel_svm_bind_mm(struct device *dev, unsigned int flags,
> if (mm) {
> ret = mmu_notifier_register(&svm->notifier, mm);
> if (ret) {
> - ioasid_free(svm->pasid);
> - kfree(svm);
> - kfree(sdev);
> + free_bind(svm, sdev, new_pasid);
> goto out;
> }
> }
> @@ -565,12 +609,18 @@ intel_svm_bind_mm(struct device *dev, unsigned int flags,
> if (ret) {
> if (mm)
> mmu_notifier_unregister(&svm->notifier, mm);
> - ioasid_free(svm->pasid);
> - kfree(svm);
> - kfree(sdev);
> + free_bind(svm, sdev, new_pasid);
> goto out;
> }
>
> + if (mm && new_pasid && !(flags & SVM_FLAG_PRIVATE_PASID)) {
> + /*
> + * Track the new pasid in the mm. The pasid will be
> + * freed at process exit. Don't track requested
> + * private PASID in the mm.
> + */
> + mm->pasid = svm->pasid;
> + }
> list_add_tail(&svm->list, &global_svm_list);
> } else {
> /*
> @@ -640,7 +690,8 @@ static int intel_svm_unbind_mm(struct device *dev, unsigned int pasid)
> kfree_rcu(sdev, rcu);
>
> if (list_empty(&svm->devs)) {
> - ioasid_free(svm->pasid);
> + /* Clear data in the pasid. */
> + ioasid_set_data(pasid, NULL);
> if (svm->mm)
> mmu_notifier_unregister(&svm->notifier, svm->mm);
> list_del(&svm->list);
> @@ -1001,3 +1052,29 @@ unsigned int intel_svm_get_pasid(struct iommu_sva *sva)
>
> return pasid;
> }
> +
> +/*
> + * An invalid pasid is either 0 (init PASID value) or bigger than max PASID
> + * (PASID_MAX - 1).
> + */
> +static bool invalid_pasid(unsigned int pasid)
> +{
> + return (pasid == INIT_PASID) || (pasid >= PASID_MAX);
> +}
> +
> +/* On process exit free the PASID (if one was allocated). */
> +void __free_pasid(struct mm_struct *mm)
> +{
> + unsigned int pasid = mm->pasid;
> +
> + /* No need to free invalid pasid. */
> + if (invalid_pasid(pasid))
> + return;
> +
> + /*
> + * Since the pasid is not bound to any svm by now, there is no race
> + * here with binding/unbinding and no need to protect the free
> + * operation by pasid_mutex.
> + */
> + ioasid_free(pasid);
> +}
>
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