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Shutemov" To: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@intel.com, luto@kernel.org, peterz@infradead.org Cc: sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com, ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com, hpa@zytor.com, jgross@suse.com, jmattson@google.com, joro@8bytes.org, jpoimboe@redhat.com, knsathya@kernel.org, pbonzini@redhat.com, sdeep@vmware.com, seanjc@google.com, tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com, thomas.lendacky@amd.com, brijesh.singh@amd.com, x86@kernel.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Subject: [PATCHv4 09/30] x86/tdx: Add MSR support for TDX guests Date: Thu, 24 Feb 2022 18:56:09 +0300 Message-Id: <20220224155630.52734-10-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220224155630.52734-1-kirill.shutemov@linux.intel.com> References: <20220224155630.52734-1-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use hypercall to emulate MSR read/write for the TDX platform. There are two viable approaches for doing MSRs in a TD guest: 1. Execute the RDMSR/WRMSR instructions like most VMs and bare metal do. Some will succeed, others will cause a #VE. All of those that cause a #VE will be handled with a TDCALL. 2. Use paravirt infrastructure. The paravirt hook has to keep a list of which MSRs would cause a #VE and use a TDCALL. All other MSRs execute RDMSR/WRMSR instructions directly. The second option can be ruled out because the list of MSRs was challenging to maintain. That leaves option #1 as the only viable solution for the minimal TDX support. For performance-critical MSR writes (like TSC_DEADLINE), future patches will replace the WRMSR/#VE sequence with the direct TDCALL. RDMSR and WRMSR specification details can be found in Guest-Host-Communication Interface (GHCI) for Intel Trust Domain Extensions (Intel TDX) specification, sec titled "TDG.VP. VMCALL" and "TDG.VP.VMCALL". Co-developed-by: Kuppuswamy Sathyanarayanan Signed-off-by: Kuppuswamy Sathyanarayanan Reviewed-by: Andi Kleen Reviewed-by: Tony Luck Signed-off-by: Kirill A. Shutemov --- arch/x86/coco/tdx.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/arch/x86/coco/tdx.c b/arch/x86/coco/tdx.c index 0a2e6be0cdae..89992593a209 100644 --- a/arch/x86/coco/tdx.c +++ b/arch/x86/coco/tdx.c @@ -116,6 +116,44 @@ void __cpuidle tdx_safe_halt(void) WARN_ONCE(1, "HLT instruction emulation failed\n"); } +static bool read_msr(struct pt_regs *regs) +{ + struct tdx_hypercall_args args = { + .r10 = TDX_HYPERCALL_STANDARD, + .r11 = EXIT_REASON_MSR_READ, + .r12 = regs->cx, + }; + + /* + * Emulate the MSR read via hypercall. More info about ABI + * can be found in TDX Guest-Host-Communication Interface + * (GHCI), section titled "TDG.VP.VMCALL". + */ + if (__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT)) + return false; + + regs->ax = lower_32_bits(args.r11); + regs->dx = upper_32_bits(args.r11); + return true; +} + +static bool write_msr(struct pt_regs *regs) +{ + struct tdx_hypercall_args args = { + .r10 = TDX_HYPERCALL_STANDARD, + .r11 = EXIT_REASON_MSR_WRITE, + .r12 = regs->cx, + .r13 = (u64)regs->dx << 32 | regs->ax, + }; + + /* + * Emulate the MSR write via hypercall. More info about ABI + * can be found in TDX Guest-Host-Communication Interface + * (GHCI) section titled "TDG.VP.VMCALL". + */ + return !__tdx_hypercall(&args, 0); +} + void tdx_get_ve_info(struct ve_info *ve) { struct tdx_module_output out; @@ -158,6 +196,10 @@ static bool virt_exception_kernel(struct pt_regs *regs, struct ve_info *ve) switch (ve->exit_reason) { case EXIT_REASON_HLT: return handle_halt(); + case EXIT_REASON_MSR_READ: + return read_msr(regs); + case EXIT_REASON_MSR_WRITE: + return write_msr(regs); default: pr_warn("Unexpected #VE: %lld\n", ve->exit_reason); return false; -- 2.34.1