From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: [PATCH] AMD/guest_iommu: Disable guest iommu support Date: Thu, 2 Oct 2014 15:02:29 +0100 Message-ID: <1412258549-18671-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Xen-devel Cc: Aravind Gopalakrishnan , Andrew Cooper , Roberto Luongo , Suravee Suthikulpanit , Jan Beulich List-Id: xen-devel@lists.xenproject.org AMD Guest IOMMU support was added to allow correct use of PASID and PRI hardware support with an ATS-aware guest driver. However, support cannot possibly function as guest_iommu_set_base() has no callers. This means that its MMIO region's P2M pages are not set to p2m_mmio_dm, preventing any invocation of the MMIO read/write handlers. c/s fd186384 "x86/HVM: extend LAPIC shortcuts around P2M lookups" introduces a path (via hvm_mmio_internal()) where iommu_mmio_handler claims its MMIO range, and causes __hvm_copy() to fail with HVMCOPY_bad_gfn_to_mfn. iommu->mmio_base defaults to 0, with a range of 8 pages, and is unilaterally enabled in any HVM guests when the host IOMMU(s) supports any extended features. Unfortunately, HVMLoader's AP boot trampoline executes an `lmsw` instruction at linear address 0x100c which unconditionally requires emulation. The instruction fetch in turn fails as __hvm_copy() fails with HVMCOPY_bad_gfn_to_mfn. The result is that multi-vcpu HVM guests do not work on newer AMD hardware, if IOMMU support is enabled in the BIOS. Change the default mmio_base address to ~0ULL. This prevents guest_iommu_mmio_range() from actually claiming any physical range whatsoever, which allows the emulation of `lmsw` to succeed. Reported-by: Roberto Luongo Suggested-by: Jan Beulich Signed-off-by: Andrew Cooper Tested-by: Roberto Luongo CC: Suravee Suthikulpanit CC: Aravind Gopalakrishnan --- xen/drivers/passthrough/amd/iommu_guest.c | 1 + 1 file changed, 1 insertion(+) diff --git a/xen/drivers/passthrough/amd/iommu_guest.c b/xen/drivers/passthrough/amd/iommu_guest.c index 5660020..98e7b38 100644 --- a/xen/drivers/passthrough/amd/iommu_guest.c +++ b/xen/drivers/passthrough/amd/iommu_guest.c @@ -885,6 +885,7 @@ int guest_iommu_init(struct domain* d) } guest_iommu_reg_init(iommu); + iommu->mmio_base = ~0ULL; iommu->domain = d; hd->arch.g_iommu = iommu; -- 1.7.10.4