From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed2-f35.google.com (mail-ed2-f35.google.com [74.125.228.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 223F337647B for ; Sat, 19 Sep 2026 22:17:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.228.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789856221; cv=none; b=eWFUXoQjkJ4kylCXPYfdLo//dvT6CQgNysnINLIgts4N9cOyjYT/w7I9dwn+A/G3BBBnhiK1/OxVlK3CzQnHgoX6ufxiR7MnDOZl3GF2HIyhiJU3BR4hej5dehyKL3sN0Y010rd4Xi+mceuoAp848/eCv8/IW3Nrt2uq729tnFo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789856221; c=relaxed/simple; bh=DQawA4FxSTUEWFv6oC2axneEjdTj8cn33tFq0Ssx89c=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=PQjMS4aaLb4K0vckGm9FF8LsIhbiDfDbHRCYLqzcfXCAwCF15Aj/qu5I/UI4iqAYC9NKOtQqME8FkZkUgmVEdocpCNtxkVeOPoqsSFkHbWltZUFj5f/i8wbd6NETYUiipAqY/fNYqXZ4blKSIXnRrzH1rGLJdXg5J9N3xCsY5AY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=cFGLtgI7; arc=none smtp.client-ip=74.125.228.99 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="cFGLtgI7" Received: by mail-ed2-f35.google.com with SMTP id 4fb4d7f45d1cf-6a64c7cdb46so2817174a12.3 for ; Sat, 19 Sep 2026 15:16:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1789856218; x=1790461018; darn=vger.kernel.org; h=cc:to:message-id:content-transfer-encoding:content-type :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to:content-type; bh=EROucbbrabZv3805uiRoXnIvZBGdkuqwaJCZzPt9pYg=; b=cFGLtgI7djzSyGHq+ZEokzc9A8RiVTfmZ6ObmabIEfTTgr9jHdOe12UEOWtd+hgtIO 026n6pnvhlXNhr8C+DchfnOICAEFWSFqr+ZLNKNN+TjMlWyUXM8FRtltb9DqNhvb4hgq oaiNFmaq1MnsxaTZL2Uhm666fmt/zdolZdcONYaLmXeEcHvYvUeSnC6R+23RwCK5WZzM ouSSwxjH/hUEUxpMk7+DKe4/uO8/LzLCaJaW2CmnyMNMqH8F9G9Ba1VuRv3qKtdET7pe EvaHc2ei9qmxZ0ZlTOUmSo6lhGTupqWfHSGnaLU8euBk7ov4peb5wo6bLVZJRK58VKow XC+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789856218; x=1790461018; h=cc:to:message-id:content-transfer-encoding:content-type :mime-version:subject:date:from:x-gm-gg:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to:content-type; bh=EROucbbrabZv3805uiRoXnIvZBGdkuqwaJCZzPt9pYg=; b=DhA55IfXXO/0KLT+5n/M9nL+WCCgnrl/tyC4Ta3jLs0YdGlPfleYvSGNBSyIhEBcA3 qKaW6E8DhzmMt0ARANhKkvU3b/tAjg6CyD2ARE2DMvQuEVFcgPvG1niMqnYc4O2Z+4r2 CPTUBZH+1pXedx9AbaHLNeKDIwHXErI52+FJlyYhzElkhSPCtbGxrFPDxapOhtnoC3sq Lfrtm52/B3bPyAnY9KGlCFJtDBL7J1/pEIjimrmEu3eutp3/hOY6sZ1oaM7dX75eP6Dt EQoJGQqs5a/w6/wM+pse/LJ8tdJcF64urNua+bF4+0/EFKk25cV6kj69GNwqa3RfYhfV 5d2Q== X-Gm-Message-State: AFuF++nBbjVg/4o24cr7BBkBvzeInMmVdR0voz4aBPtU4NumkjZxgxYw u2iLPYt7T3kp3SuTIvsLVLDDtbVVNXlXexdPNxN43k6CNJXgLbL+8x1B X-Gm-Gg: AYBFou13aZ74ghvtw1kgP3JCNqom9Ff3CuYyEGnQRw7nRPdsDuXFN8oOY7gQeygtw6/ /HPEFR8Znqi6+U2W31m7occ7iF7Jjv8qWu7V5L8OLZ1Z3IiB+Avc6sdZHYtjJACjfjyZEKYFzcR 4zhupr+nkU4bpV5rRyXYhIIhF/s/Q9dOz1/05wI4zW6Mr88M9fT1T9jhzvHUgeYqa0MBSURvHcT XUSaGTT/gdHEx3HXM6eoifKG4nlQ/W3iyrafkdtgHTrrXL/qEbWIRwpPaAe697mr9oEQl6flUHg TALHcr77MCdXgZvjg2A0HjQG/qDOtpsqW3FWdxebEmkbD4GrE26hIqQAQ0HAeJ6GcyhdQWzEbND 8KOUQuY7KuJLxvh2xmMxPDgdnwC5SZnD1OYWnAU5VCPj2ZlM3frFMN0//vyZG4j/RLqhE/cRZD8 Bn0wfbvrOx7acT72kxsX6SMZGMXPWLaSC2vP1ZrMECIGAi5WDvSukMA5VOHeV26T7+dLHorA== X-Received: by 2002:a05:6402:44c2:b0:6a8:118:9592 with SMTP id 4fb4d7f45d1cf-6aa565010d5mr3268995a12.16.1789856217535; Sat, 19 Sep 2026 15:16:57 -0700 (PDT) Received: from localhost ([2a03:2880:32ff:6::]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6aa67dc582csm1766619a12.16.2026.09.19.15.16.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 15:16:57 -0700 (PDT) From: Samuel Crossley Date: Sat, 19 Sep 2026 15:13:03 -0700 Subject: [PATCH v2] vfio/type1: avoid walking reserved-only mappings while unpinning Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260919-vfio-v2-1-68e7ed355972@gmail.com> X-B4-Tracking: v=1; b=H4sIAO4Ir2oC/12NwQ6DIBAFf4XsWRrBiNVT/6PxoLDoNlUMWNLG8 O8N9tbjS+bNHBDQEwbo2AEeIwVyK3RMFgz0PKwTcjLQMZClVGUjKx4tOW5Qm6sabaWtgoLB5tH S+9Tc+98Or/GBes/fTMwUduc/ZyeKzP0po+CCV2Pd1k3bCqXVbVoGel60W6BPKX0BF0UewKoAA AA= X-Change-ID: 20260723-vfio-decd86bf3cf6 To: Alex Williamson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Samuel Crossley X-Mailer: b4 0.16-dev Tearing down a large device-passthrough DMA mapping can process tens of millions of reserved pfns in a single VFIO_IOMMU_UNMAP_DMA. A 128 GiB reserved mapping holds about 33.6 million 4KiB pfns, and vfio_unpin_pages_remote() walks every one of them whenever dma->has_rsvd is set, because reserved and non-reserved pfns might be mixed. For a mapping that contains only reserved pfns every put_pfn() is a no-op, but each one still pays for the pfn_valid()/PageReserved() classification. Seen on GPU-passthrough hosts running 6.13 with the v6.18 type1 series backported, where a single VFIO_IOMMU_UNMAP_DMA held a CPU past the soft-lockup watchdog (host identification, register dump and module list trimmed): watchdog: BUG: soft lockup - CPU#261 stuck for 22s! [qemu-system-x86:134503] RIP: 0010:vfio_unpin_pages_remote+0x139/0x2a0 [vfio_iommu_type1] Code: 90 4c 89 e1 48 c1 e9 34 75 74 4c 89 e1 48 c1 e9 22 75 6b 48 8b 0d f7 6f c2 e3 48 85 c9 74 5f 4c 89 e2 48 c1 ea 16 48 8b 0c d1 <48> 85 c9 74 4f 41 8b 55 30 4c 89 e6 48 c1 ee 0f 83 e6 7f c1 e6 05 Call Trace: ? watchdog_timer_fn+0x3d6/0x440 ? running_clock+0x10/0x10 ? hrtimer_interrupt+0x185/0x580 ? __sysvec_apic_timer_interrupt+0x44/0xe0 ? sysvec_apic_timer_interrupt+0x6b/0x80 ? asm_sysvec_apic_timer_interrupt+0x16/0x20 ? vfio_unpin_pages_remote+0x139/0x2a0 [vfio_iommu_type1] vfio_sync_unpin+0x96/0xf0 [vfio_iommu_type1] vfio_unmap_unpin+0x324/0x3d0 [vfio_iommu_type1] vfio_remove_dma+0x25/0xa0 [vfio_iommu_type1] vfio_iommu_type1_ioctl+0xcd5/0x1760 [vfio_iommu_type1] ? amd_pmu_v2_enable_all+0xa/0x30 ? perf_pmu_sched_task+0xbf/0xf0 x64_sys_call+0x282/0x1ac0 ? syscall_trace_enter+0x1e5/0x1f0 do_syscall_64+0x68/0x130 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP is the mem_section root test in pfn_valid(), inlined into put_pfn() through is_invalid_reserved_pfn(), so the stall is in the dma->has_rsvd per-page loop. mem_section[] has no root for that pfn, so pfn_valid() returns false and put_pfn() does nothing - for every pfn in the mapping. Track whether the mapping also contains non-reserved pfns and skip the walk entirely for reserved-only mappings. Mixed mappings keep the existing per-pfn walk, and ordinary mappings keep the existing batched unpin path. Tested on an affected host: reserved-only mappings up to 128 GiB take the new path and complete in microseconds. The ordinary-page path was exercised unchanged. Suggested-by: Alex Williamson Link: https://lore.kernel.org/all/20260803154707.71cc0d6b@shazbot.org/ Signed-off-by: Samuel Crossley --- This is the reserved-only fast path you suggested on v1, tested on the affected hosts. There is indeed no evidence that the non-reserved VFIO path needs chunking, and agree any such change to unpin_user_page_range_dirty_lock() would belong in mm, so not including it in this patch. --- Changes in v2: - Replace v1's cond_resched() chunking with the reserved-only fast path. - Tested on an affected host; reserved-only mappings up to 128 GiB now complete in microseconds instead of walking ~33.6M pfns. - Link to v1: https://patch.msgid.link/20260723-vfio-v1-1-3b59579916c6@gmail.com --- drivers/vfio/vfio_iommu_type1.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index c8151ba54de3..f7addfbe1aab 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -94,6 +94,7 @@ struct vfio_dma { bool lock_cap; /* capable(CAP_IPC_LOCK) */ bool vaddr_invalid; bool has_rsvd; /* has 1 or more rsvd pfns */ + bool has_non_rsvd; /* has 1 or more !rsvd pfns */ struct task_struct *task; struct rb_root pfn_list; /* Ex-user pinned pfn list */ unsigned long *bitmap; @@ -791,6 +792,7 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr, out: dma->has_rsvd |= rsvd; + dma->has_non_rsvd |= !rsvd; ret = vfio_lock_acct(dma, lock_acct, false); unpin_out: @@ -821,11 +823,13 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova, long unlocked = 0, locked = vpfn_pages(dma, iova, npage); if (dma->has_rsvd) { - unsigned long i; + if (dma->has_non_rsvd) { + unsigned long i; - for (i = 0; i < npage; i++) - if (put_pfn(pfn++, dma->prot)) - unlocked++; + for (i = 0; i < npage; i++) + if (put_pfn(pfn++, dma->prot)) + unlocked++; + } } else { put_valid_unreserved_pfns(pfn, npage, dma->prot); unlocked = npage; --- base-commit: 4e3c1fc8abcb8eff062150b4340fa4569696d645 change-id: 20260723-vfio-decd86bf3cf6 Best regards, -- Samuel Crossley