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
32 lines
676 B
C
32 lines
676 B
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) 2018, Red Hat, Inc.
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*/
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#include "kvm_util.h"
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#define UCALL_PIO_PORT ((uint16_t)0x1000)
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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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void ucall_arch_do_ucall(vm_vaddr_t uc)
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{
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asm volatile("in %[port], %%al"
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: : [port] "d" (UCALL_PIO_PORT), "D" (uc) : "rax", "memory");
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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_IO && run->io.port == UCALL_PIO_PORT) {
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struct kvm_regs regs;
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vcpu_regs_get(vcpu, ®s);
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return (void *)regs.rdi;
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}
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return NULL;
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}
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