From 08c2336df78d01fd4d634b14262ea739c399ddbd Mon Sep 17 00:00:00 2001 From: Brijesh Singh Date: Tue, 24 Aug 2021 11:04:35 +0000 Subject: [PATCH] x86/kvm: Add AMD SEV specific Hypercall3 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 Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Paolo Bonzini Cc: Joerg Roedel Cc: Borislav Petkov Cc: Tom Lendacky Cc: x86@kernel.org Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Reviewed-by: Steve Rutherford Reviewed-by: Venu Busireddy Signed-off-by: Brijesh Singh Signed-off-by: Ashish Kalra Message-Id: <6fd25c749205dd0b1eb492c60d41b124760cc6ae.1629726117.git.ashish.kalra@amd.com> Signed-off-by: Paolo Bonzini --- arch/x86/include/asm/kvm_para.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h index 6929987..56935eb 100644 --- a/arch/x86/include/asm/kvm_para.h +++ b/arch/x86/include/asm/kvm_para.h @@ -83,6 +83,18 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1, return ret; } +static inline long kvm_sev_hypercall3(unsigned int nr, unsigned long p1, + unsigned long p2, unsigned long p3) +{ + long ret; + + asm volatile("vmmcall" + : "=a"(ret) + : "a"(nr), "b"(p1), "c"(p2), "d"(p3) + : "memory"); + return ret; +} + #ifdef CONFIG_KVM_GUEST void kvmclock_init(void); void kvmclock_disable(void); -- 2.7.4