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BL1PR12MB5064.namprd12.prod.outlook.com (2603:10b6:208:30a::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7202.34; Mon, 22 Jan 2024 09:18:20 +0000 Received: from PH7PR12MB5685.namprd12.prod.outlook.com ([fe80::e1fb:4123:48b1:653]) by PH7PR12MB5685.namprd12.prod.outlook.com ([fe80::e1fb:4123:48b1:653%4]) with mapi id 15.20.7202.031; Mon, 22 Jan 2024 09:18:20 +0000 Message-ID: <5ed7d46b-ae26-43f2-81e0-91e3cfc0218a@amd.com> Date: Mon, 22 Jan 2024 10:18:01 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Remove double faults once write a device pfn Content-Language: en-US To: Xianrong Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: luto@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, alexander.deucher@amd.com, Xinhui.Pan@amd.com, airlied@gmail.com, daniel@ffwll.ch, jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, 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qPhYVuK3Ty62aVYbvWJJoF7YKdltOxsnIEiN/L7z9YjCaNakgPalhNwV8mkcwccVohIXfWH355nnlo2zCxIHnd4do7Lc5Qrl3RYeUhgXc4Sff6gM1lnOaOnSL+ValwZ9HqeI6bIteI9Z8dInOtWc1OJdLgGGeAlYLfZtN3VKm1lub7h8sx8ssbDyUvR60iUuhCWPUaKOAel+D846GwblxFTzahh0TusZwsgYfl5FRyNijFe7/LYOrKSbuJocSN5bKzlfgvAfVzKPtzsbLLTCIift7SEv8LER/YoIu X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Am 22.01.24 um 04:32 schrieb Xianrong Zhou: > The vmf_insert_pfn_prot could cause unnecessary double faults > on a device pfn. Because currently the vmf_insert_pfn_prot does > not make the pfn writable so the pte entry is normally read-only > or dirty catching. What? How do you got to this conclusion? > The first fault only sets up the pte entry which actually is > dirty catching. And the second immediate fault to the pfn due > to first dirty catching when the cpu re-execute the store > instruction. It could be that this is done to work around some hw behavior, but not because of dirty catching. > Normally if the drivers call vmf_insert_pfn_prot and also supply > 'pfn_mkwrite' callback within vm_operations_struct which requires > the pte to be dirty catching then the vmf_insert_pfn_prot and the > double fault are reasonable. It is not a problem. Well, as far as I can see that behavior absolutely doesn't make sense. When pfn_mkwrite is requested then the driver should use PAGE_COPY, which is exactly what VMWGFX (the only driver using dirty tracking) is doing. Everybody else uses PAGE_SHARED which should make the pte writeable immediately. Regards, Christian. > > However the most of drivers calling vmf_insert_pfn_prot do not > supply the 'pfn_mkwrite' callback so that the second fault is > unnecessary. > > So just like vmf_insert_mixed and vmf_insert_mixed_mkwrite pair, > we should also supply vmf_insert_pfn_mkwrite for drivers as well. > > Signed-off-by: Xianrong Zhou > --- > arch/x86/entry/vdso/vma.c | 3 ++- > drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 2 +- > drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 2 +- > drivers/gpu/drm/nouveau/nouveau_gem.c | 2 +- > drivers/gpu/drm/radeon/radeon_gem.c | 2 +- > drivers/gpu/drm/ttm/ttm_bo_vm.c | 8 +++++--- > drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c | 8 +++++--- > include/drm/ttm/ttm_bo.h | 3 ++- > include/linux/mm.h | 2 +- > mm/memory.c | 14 +++++++++++--- > 10 files changed, 30 insertions(+), 16 deletions(-) > > diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c > index 7645730dc228..dd2431c2975f 100644 > --- a/arch/x86/entry/vdso/vma.c > +++ b/arch/x86/entry/vdso/vma.c > @@ -185,7 +185,8 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm, > if (pvti && vclock_was_used(VDSO_CLOCKMODE_PVCLOCK)) { > return vmf_insert_pfn_prot(vma, vmf->address, > __pa(pvti) >> PAGE_SHIFT, > - pgprot_decrypted(vma->vm_page_prot)); > + pgprot_decrypted(vma->vm_page_prot), > + true); > } > } else if (sym_offset == image->sym_hvclock_page) { > pfn = hv_get_tsc_pfn(); > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c > index 49a5f1c73b3e..adcb20d9e624 100644 > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c > @@ -64,7 +64,7 @@ static vm_fault_t amdgpu_gem_fault(struct vm_fault *vmf) > } > > ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot, > - TTM_BO_VM_NUM_PREFAULT); > + TTM_BO_VM_NUM_PREFAULT, true); > > drm_dev_exit(idx); > } else { > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > index 9227f8146a58..c6f13ae6c308 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c > @@ -1114,7 +1114,7 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf) > > if (drm_dev_enter(dev, &idx)) { > ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot, > - TTM_BO_VM_NUM_PREFAULT); > + TTM_BO_VM_NUM_PREFAULT, true); > drm_dev_exit(idx); > } else { > ret = ttm_bo_vm_dummy_page(vmf, vmf->vma->vm_page_prot); > diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c > index 49c2bcbef129..7e1453762ec9 100644 > --- a/drivers/gpu/drm/nouveau/nouveau_gem.c > +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c > @@ -56,7 +56,7 @@ static vm_fault_t nouveau_ttm_fault(struct vm_fault *vmf) > > nouveau_bo_del_io_reserve_lru(bo); > prot = vm_get_page_prot(vma->vm_flags); > - ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT); > + ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, true); > nouveau_bo_add_io_reserve_lru(bo); > if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) > return ret; > diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c > index 3fec3acdaf28..b21cf00ae162 100644 > --- a/drivers/gpu/drm/radeon/radeon_gem.c > +++ b/drivers/gpu/drm/radeon/radeon_gem.c > @@ -62,7 +62,7 @@ static vm_fault_t radeon_gem_fault(struct vm_fault *vmf) > goto unlock_resv; > > ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot, > - TTM_BO_VM_NUM_PREFAULT); > + TTM_BO_VM_NUM_PREFAULT, true); > if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) > goto unlock_mclk; > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c > index 4212b8c91dd4..7d14a7d267aa 100644 > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c > @@ -167,6 +167,7 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve); > * @num_prefault: Maximum number of prefault pages. The caller may want to > * specify this based on madvice settings and the size of the GPU object > * backed by the memory. > + * @mkwrite: make the pfn or page writable > * > * This function inserts one or more page table entries pointing to the > * memory backing the buffer object, and then returns a return code > @@ -180,7 +181,8 @@ EXPORT_SYMBOL(ttm_bo_vm_reserve); > */ > vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, > pgprot_t prot, > - pgoff_t num_prefault) > + pgoff_t num_prefault, > + bool mkwrite) > { > struct vm_area_struct *vma = vmf->vma; > struct ttm_buffer_object *bo = vma->vm_private_data; > @@ -263,7 +265,7 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, > * at arbitrary times while the data is mmap'ed. > * See vmf_insert_pfn_prot() for a discussion. > */ > - ret = vmf_insert_pfn_prot(vma, address, pfn, prot); > + ret = vmf_insert_pfn_prot(vma, address, pfn, prot, mkwrite); > > /* Never error on prefaulted PTEs */ > if (unlikely((ret & VM_FAULT_ERROR))) { > @@ -312,7 +314,7 @@ vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot) > /* Prefault the entire VMA range right away to avoid further faults */ > for (address = vma->vm_start; address < vma->vm_end; > address += PAGE_SIZE) > - ret = vmf_insert_pfn_prot(vma, address, pfn, prot); > + ret = vmf_insert_pfn_prot(vma, address, pfn, prot, true); > > return ret; > } > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c > index 74ff2812d66a..bb8e4b641681 100644 > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c > @@ -452,12 +452,14 @@ vm_fault_t vmw_bo_vm_fault(struct vm_fault *vmf) > * sure the page protection is write-enabled so we don't get > * a lot of unnecessary write faults. > */ > - if (vbo->dirty && vbo->dirty->method == VMW_BO_DIRTY_MKWRITE) > + if (vbo->dirty && vbo->dirty->method == VMW_BO_DIRTY_MKWRITE) { > prot = vm_get_page_prot(vma->vm_flags & ~VM_SHARED); > - else > + ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault, false); > + } else { > prot = vm_get_page_prot(vma->vm_flags); > + ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault, true); > + } > > - ret = ttm_bo_vm_fault_reserved(vmf, prot, num_prefault); > if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) > return ret; > > diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h > index 0223a41a64b2..66e293db69ee 100644 > --- a/include/drm/ttm/ttm_bo.h > +++ b/include/drm/ttm/ttm_bo.h > @@ -386,7 +386,8 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo, > struct vm_fault *vmf); > vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, > pgprot_t prot, > - pgoff_t num_prefault); > + pgoff_t num_prefault, > + bool mkwrite); > vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf); > void ttm_bo_vm_open(struct vm_area_struct *vma); > void ttm_bo_vm_close(struct vm_area_struct *vma); > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f5a97dec5169..f8868e28ea04 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3553,7 +3553,7 @@ int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages, > vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn); > vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > - unsigned long pfn, pgprot_t pgprot); > + unsigned long pfn, pgprot_t pgprot, bool mkwrite); > vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr, > pfn_t pfn); > vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma, > diff --git a/mm/memory.c b/mm/memory.c > index 7e1f4849463a..2c28f1a349ff 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2195,6 +2195,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr, > * @addr: target user address of this page > * @pfn: source kernel pfn > * @pgprot: pgprot flags for the inserted page > + * @mkwrite: make the pfn writable > * > * This is exactly like vmf_insert_pfn(), except that it allows drivers > * to override pgprot on a per-page basis. > @@ -2223,7 +2224,7 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr, > * Return: vm_fault_t value. > */ > vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > - unsigned long pfn, pgprot_t pgprot) > + unsigned long pfn, pgprot_t pgprot, bool mkwrite) > { > /* > * Technically, architectures with pte_special can avoid all these > @@ -2246,7 +2247,7 @@ vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV)); > > return insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot, > - false); > + mkwrite); > } > EXPORT_SYMBOL(vmf_insert_pfn_prot); > > @@ -2273,10 +2274,17 @@ EXPORT_SYMBOL(vmf_insert_pfn_prot); > vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn) > { > - return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot); > + return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot, false); > } > EXPORT_SYMBOL(vmf_insert_pfn); > > +vm_fault_t vmf_insert_pfn_mkwrite(struct vm_area_struct *vma, unsigned long addr, > + unsigned long pfn) > +{ > + return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot, true); > +} > +EXPORT_SYMBOL(vmf_insert_pfn_mkwrite); > + > static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn) > { > /* these checks mirror the abort conditions in vm_normal_page */