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08c2336df7
KVM hypercall framework relies on alternative framework to patch the VMCALL -> VMMCALL on AMD platform. If a hypercall is made before apply_alternative() is called then it defaults to VMCALL. The approach works fine on non SEV guest. A VMCALL would causes #UD, and hypervisor will be able to decode the instruction and do the right things. But when SEV is active, guest memory is encrypted with guest key and hypervisor will not be able to decode the instruction bytes. To highlight the need to provide this interface, capturing the flow of apply_alternatives() : setup_arch() call init_hypervisor_platform() which detects the hypervisor platform the kernel is running under and then the hypervisor specific initialization code can make early hypercalls. For example, KVM specific initialization in case of SEV will try to mark the "__bss_decrypted" section's encryption state via early page encryption status hypercalls. Now, apply_alternatives() is called much later when setup_arch() calls check_bugs(), so we do need some kind of an early, pre-alternatives hypercall interface. Other cases of pre-alternatives hypercalls include marking per-cpu GHCB pages as decrypted on SEV-ES and per-cpu apf_reason, steal_time and kvm_apic_eoi as decrypted for SEV generally. Add SEV specific hypercall3, it unconditionally uses VMMCALL. The hypercall will be used by the SEV guest to notify encrypted pages to the hypervisor. This kvm_sev_hypercall3() function is abstracted and used as follows : All these early hypercalls are made through early_set_memory_XX() interfaces, which in turn invoke pv_ops (paravirt_ops). This early_set_memory_XX() -> pv_ops.mmu.notify_page_enc_status_changed() is a generic interface and can easily have SEV, TDX and any other future platform specific abstractions added to it. Currently, pv_ops.mmu.notify_page_enc_status_changed() callback is setup to invoke kvm_sev_hypercall3() in case of SEV. Similarly, in case of TDX, pv_ops.mmu.notify_page_enc_status_changed() can be setup to a TDX specific callback. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Borislav Petkov <bp@suse.de> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: x86@kernel.org Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Reviewed-by: Steve Rutherford <srutherford@google.com> Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com> Message-Id: <6fd25c749205dd0b1eb492c60d41b124760cc6ae.1629726117.git.ashish.kalra@amd.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.