426729b2cf
To play nice with guests whose stack memory is encrypted, e.g. AMD SEV, introduce a new "ucall pool" implementation that passes the ucall struct via dedicated memory (which can be mapped shared, a.k.a. as plain text). Because not all architectures have access to the vCPU index in the guest, use a bitmap with atomic accesses to track which entries in the pool are free/used. A list+lock could also work in theory, but synchronizing the individual pointers to the guest would be a mess. Note, there's no need to rewalk the bitmap to ensure success. If all vCPUs are simply allocating, success is guaranteed because there are enough entries for all vCPUs. If one or more vCPUs are freeing and then reallocating, success is guaranteed because vCPUs _always_ walk the bitmap from 0=>N; if vCPU frees an entry and then wins a race to re-allocate, then either it will consume the entry it just freed (bit is the first free bit), or the losing vCPU is guaranteed to see the freed bit (winner consumes an earlier bit, which the loser hasn't yet visited). Reviewed-by: Andrew Jones <andrew.jones@linux.dev> Signed-off-by: Peter Gonda <pgonda@google.com> Co-developed-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Link: https://lore.kernel.org/r/20221006003409.649993-8-seanjc@google.com
68 lines
1.7 KiB
C
68 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* ucall support. A ucall is a "hypercall to userspace".
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*
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* Copyright (C) 2021 Western Digital Corporation or its affiliates.
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*/
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#include <linux/kvm.h>
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#include "kvm_util.h"
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#include "processor.h"
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void ucall_arch_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa)
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{
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}
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struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0,
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unsigned long arg1, unsigned long arg2,
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unsigned long arg3, unsigned long arg4,
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unsigned long arg5)
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{
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register uintptr_t a0 asm ("a0") = (uintptr_t)(arg0);
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register uintptr_t a1 asm ("a1") = (uintptr_t)(arg1);
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register uintptr_t a2 asm ("a2") = (uintptr_t)(arg2);
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register uintptr_t a3 asm ("a3") = (uintptr_t)(arg3);
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register uintptr_t a4 asm ("a4") = (uintptr_t)(arg4);
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register uintptr_t a5 asm ("a5") = (uintptr_t)(arg5);
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register uintptr_t a6 asm ("a6") = (uintptr_t)(fid);
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register uintptr_t a7 asm ("a7") = (uintptr_t)(ext);
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struct sbiret ret;
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asm volatile (
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"ecall"
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: "+r" (a0), "+r" (a1)
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: "r" (a2), "r" (a3), "r" (a4), "r" (a5), "r" (a6), "r" (a7)
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: "memory");
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ret.error = a0;
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ret.value = a1;
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return ret;
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}
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void ucall_arch_do_ucall(vm_vaddr_t uc)
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{
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sbi_ecall(KVM_RISCV_SELFTESTS_SBI_EXT,
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KVM_RISCV_SELFTESTS_SBI_UCALL,
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uc, 0, 0, 0, 0, 0);
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}
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void *ucall_arch_get_ucall(struct kvm_vcpu *vcpu)
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{
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struct kvm_run *run = vcpu->run;
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if (run->exit_reason == KVM_EXIT_RISCV_SBI &&
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run->riscv_sbi.extension_id == KVM_RISCV_SELFTESTS_SBI_EXT) {
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switch (run->riscv_sbi.function_id) {
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case KVM_RISCV_SELFTESTS_SBI_UCALL:
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return (void *)run->riscv_sbi.args[0];
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case KVM_RISCV_SELFTESTS_SBI_UNEXP:
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vcpu_dump(stderr, vcpu, 2);
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TEST_ASSERT(0, "Unexpected trap taken by guest");
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break;
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default:
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break;
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}
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}
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return NULL;
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}
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