On 05/23/2012 05:08 PM, Gleb Natapov wrote:
> "rep ins" emulation is going through emulator now. This is slow because
> emulator knows how to write back only one datum at a time. This patch
> provides fast path for the instruction in certain conditions. The
> conditions are: DF flag is not set, destination memory is RAM and single
> datum does not cross page boundary. If fast path code fails it falls
> back to emulation.
>
>
> +static int __kvm_fast_string_pio_in(struct kvm_vcpu *vcpu, int size,
> + unsigned short port, unsigned long addr,
> + int count)
> +{
> + struct page *page;
> + gpa_t gpa;
> + char *kaddr;
> + int ret;
> +
> + gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, NULL);
> +
> + if (gpa == UNMAPPED_GVA ||
> + (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
> + return EMULATE_FAIL;
> +
> + page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
> + if (is_error_page(page)) {
> + kvm_release_page_clean(page);
> + return EMULATE_FAIL;
> + }
> +
> + kaddr = kmap_atomic(page);
> + kaddr += offset_in_page(gpa);
> +
> + ret = emulator_pio_in_emulated(&vcpu->arch.emulate_ctxt, size, port,
> + kaddr, count);
> +
> + kunmap_atomic(kaddr);
> + if (ret) {
> + kvm_register_write(vcpu, VCPU_REGS_RCX,
> + kvm_register_read(vcpu, VCPU_REGS_RCX) - count);
Sometimes we only modify the low 16 bits of %rcx.
> + kvm_register_write(vcpu, VCPU_REGS_RDI,
> + kvm_register_read(vcpu, VCPU_REGS_RDI) + count*size);
Possibly, ditto.
> + kvm_release_page_dirty(page);
> + return EMULATE_DONE;
> + }
> + kvm_release_page_clean(page);
> + return EMULATE_DO_MMIO;
> +}
> +
> +
> +int kvm_fast_string_pio_in(struct kvm_vcpu *vcpu, int size,
> + unsigned short port, u8 addr_size)
This is actually the logarithm of addr_size, the variable name should
reflect it.
> +{
> + unsigned long masks[] = {0xffff, 0xffffffff, ~0};
> + unsigned long rdi = kvm_register_read(vcpu, VCPU_REGS_RDI);
> + unsigned long linear_addr = rdi + get_segment_base(vcpu, VCPU_SREG_ES);
> + unsigned long rcx = kvm_register_read(vcpu, VCPU_REGS_RCX), count;
> + int r;
> +
Missing es limit check - rep in can succeed for part of the page, fail
when the %rdi hits the limit.
> + if (rcx == 0) {
> + kvm_x86_ops->skip_emulated_instruction(vcpu);
> + return EMULATE_DONE;
> + }
> + if (kvm_get_rflags(vcpu) & X86_EFLAGS_DF)
> + return EMULATE_FAIL;
> + if (addr_size > 2)
> + return EMULATE_FAIL;
> +
> + linear_addr &= masks[addr_size];
Also need to mask %rcx.
> +
> + count = (PAGE_SIZE - offset_in_page(linear_addr))/size;
> +
> + if (count == 0) /* 'in' crosses page boundry */
> + return EMULATE_FAIL;
> +
> + count = min(count, rcx);
> +
> + r = __kvm_fast_string_pio_in(vcpu, size, port, linear_addr, count);
> +
> + if (r != EMULATE_DO_MMIO)
> + return r;
> +
> + vcpu->arch.fast_string_pio_ctxt.linear_addr = linear_addr;
> + vcpu->arch.complete_userspace_io = complete_fast_string_pio;
> + return EMULATE_DO_MMIO;
> +}
> +EXPORT_SYMBOL_GPL(kvm_fast_string_pio_in);
Perhaps a better way to do it is to move the code into the emulator,
which already handles all the checks and masks, and just avoid
x86_decode_insn()/x86_emulate_insn().
> +
> static void tsc_bad(void *info)
> {
> __this_cpu_write(cpu_tsc_khz, 0);
--
error compiling committee.c: too many arguments to function
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