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AJvYcCXO8KEXtVJWPC2qmLVXhYXioABsReNBiRtEnwt6wZ5sSM5aY6N9ikY+zopxiFTvg/+6MyJxyAunYA==@kvack.org X-Gm-Message-State: AOJu0YyIVyz4Mu/rdg02kFc1zYOARuETr6hbfOrEbZokNASTIO7FliTP 3dMxtiDOX2Bn0EF8Xq8b9XLSKQ5bNAooBN4+xdNkR1xnwXHOZqIRYqKl2/loRBFrou0XYjrUIYT 4CKRngAuuXWoBGyOY9es7KE9rUR5K8w== X-Google-Smtp-Source: AGHT+IERD+l6Qr6J2S5605UuPiCiMcftraa9jRU70etne+wWJmsgybVfSfST3MV8N0dT1RzxzjB3D97djZCg9uFGd0I= X-Received: by 2002:a2e:b88a:0:b0:2ff:55a0:91ff with SMTP id 38308e7fff4ca-2ff6064e115mr51444081fa.3.1731952843968; Mon, 18 Nov 2024 10:00:43 -0800 (PST) MIME-Version: 1.0 From: Ajay Garg Date: Mon, 18 Nov 2024 23:30:32 +0530 Message-ID: Subject: Queries regarding consolidated picture of virtualization and SPT/EPT/IOMMU/DMAR/PT To: Linux Kernel Mailing List , iommu@lists.linux-foundation.org, kvm@vger.kernel.org, Linux Memory Management List Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 979DDC0030 X-Stat-Signature: zsd6yaif4bop9xkuttjxn37r3psmmwia X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1731952824-240550 X-HE-Meta: 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 fh46Ub9Y LUoI/kMPRtRN5yj0JcmvP0cAvo8Vg6QkTQUn1HFi0ZeA5Xr2WueczJhEfURAhz/ObXm7gtL3mi4OrkZyV1ReLlKbiiuZYrixhP3QjTtwiDEgo3Wx2Z5itPT8DEm+osEUePMny3lOjvLZezmVtmF0hIxRH5N/nYBvjXCcpCRAfPQ2FK3ZENbRQAXCx2taFlUi6+LHKs5/vO7i3v9J2LqtELMQOTKIe5baQirbMqLfLyA/a7aIIJ/f3NSE316Nma6/VhO5vcNQYehU3oyngGrP5i0bv4Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.001123, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi everyone. I understand in a para-virtualization environment, VMM maintains a shadow-page-table (SPT) per process per guest, for GVA => HPA translation. The hardware/MMU is passed a single pointer to this shadow-page-table. The guest is aware that it is running in a virtualization environment, and communicates with VMM to help maintain the shadow-page-table. In full-virtualization/HVM virtualization, the guest is unaware that it is running in a virtualized environment, and all GVA => GPA are private. The VMM is obviously aware of all HVA => HPA mappings; plus GPA => HVA is trivial as it's only an offset difference (Extended Page Table, EPT). The hardware/MMU is passed three things : * Pointer to guest page-table, for GVA => GPA. * Offset, for GPA => HVA. * Pointer to host page-table, for HVA => HPA. In both the above cases, DMA is a challenge (without IOMMU), as device-addresses would need to be physically-contiguous. This would in turn mean that all of GPA needs to be physically-contiguous, which in turn means that the host would need to spawn guest-process with all of memory (HVA) which is physically-contiguous - very hard to meet generally. *_Kindly correct me if I have made a mistake so far at conceptual level._* Now, enters IOMMU, providing the ability to DMA with non-contiguous device-addresses. Now, my queries are simple : * Is IOMMU DMA-Remapping mode (DMAR) analogous to a para-virtualization environment (as per previous brief context)? * Is IOMMU Pass-through (PT) mode analogous to a HVM environment (as per previous brief context)? Many thanks in advance for your time; hopefully I have not been a complete idiot .. Thanks and Regards, Ajay