Marcelo Tosatti wrote:
> Emulate cmpxchg8b atomically on i386. This is required to avoid a guest
> pte walker from seeing a splitted write.
>
> Signed-off-by: Marcelo Tosatti <[EMAIL PROTECTED]>
>
> diff --git a/drivers/kvm/x86.c b/drivers/kvm/x86.c
> index 9db4e32..d58d795 100644
> --- a/drivers/kvm/x86.c
> +++ b/drivers/kvm/x86.c
> @@ -1674,6 +1674,33 @@ static int emulator_cmpxchg_emulated(uns
> reported = 1;
> printk(KERN_WARNING "kvm: emulating exchange as write\n");
> }
> +#ifndef CONFIG_X86_64
> + /* guests cmpxchg8b have to be emulated atomically */
> + if (bytes == 8) {
> + gpa_t gpa = vcpu->mmu.gva_to_gpa(vcpu, addr);
> + struct page *page;
> + char *addr;
> + u64 *val;
> +
> + if (gpa == UNMAPPED_GVA ||
> + (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
> + goto emul_write;
> +
> + val = (u64 *)new;
> + page = gfn_to_page(page, gpa >> PAGE_SHIFT);
> + addr = kmap_atomic(page, KM_USER0);
> + addr += offset_in_page(gpa);
> +
> + set_64bit((unsigned long long *)addr, val);
> +
> + kunmap_atomic(page, KM_USER0);
> + kvm_release_page_dirty(page);
> +
> + return X86EMUL_CONTINUE;
> + }
> +#endif
> +
> +emul_write:
> return emulator_write_emulated(addr, new, bytes, vcpu);
> }
>
Won't the compiler complain when it sees an unreferenced label?
Also, we should handle the page boundary crossing case (probably by just
emulating as a write and crosssing fingers).
--
Any sufficiently difficult bug is indistinguishable from a feature.
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