linux-kernel - Re: [RFC v2 14/32] x86/tdx: Handle port I/O

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Date:   Tue, 11 May 2021 08:08:20 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2 14/32] x86/tdx: Handle port I/O



On 5/11/21 7:39 AM, Dave Hansen wrote:
> To what you do you refer by "this patch allocates this memory in ASM
> code"?  Could you point to the specific ASM code that "allocates memory"?

We use 40 bytes in stack for storing the output register values. It is in
function tdg_inl().

subq $TDVMCALL_OUTPUT_SIZE, %rsp

+SYM_FUNC_START(tdg_inl)
+	io_save_registers
+	/* Set data width to 4 bytes */
+	mov $4, %rsi
+1:
+	mov %rdx, %rcx
+	/* Set 0 in RDX to select in operation */
+	mov $0, %rdx
+	/* Set TDVMCALL function id in RDI */
+	mov $EXIT_REASON_IO_INSTRUCTION, %rdi
+	/* Set TDVMCALL type info (0 - Standard, > 0 - vendor) in R10 */
+	xor %r10, %r10
+	/* Allocate memory in stack for Output */
+	subq $TDVMCALL_OUTPUT_SIZE, %rsp
+	/* Move tdvmcall_output pointer to R9 */
+	movq %rsp, %r9
+
+	call do_tdvmcall

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer