Re: [PATCH 7/24] Understanding guest pointers to vmcs12 structures

["Nadav Har'El" <nyh@math.technion.ac.il>]

On Sun, Aug 01, 2010, Gleb Natapov wrote about "Re: [PATCH 7/24] Understanding guest pointers to vmcs12 structures":
> Guest can use any valid virtual address. There is UNMAPPED_GVA (~(gpa_t)0) which
> at least cannot be valid if address that your function returns have to be
> page aligned.

Thanks. Unfortunately, I also use this function to decode non-page-aligned
addresses (such as an address given to VMWRITE to take a value from), so I
cannot use this nice trick.

> And not all virtual addresses are valid BTW. For 32 bit
> guest virt address cannot be bigger then 32 bit and for 64 bit guest
> virtual address should be in canonical form.

I guess this means that I can easily find a gva_t which is always invalid -
e.g., 1<<63 isn't a legal 32-bit address (of course), and also isn't a legal
canonical-form 64 (or rather 48)-bit address - so I could use that as a flag.

But I decided that to make things clearer, I'll change the function to return
a success flag, and return the gva_t itself into a given pointer:

static int get_vmx_mem_address(struct kvm_vcpu *vcpu,
                                 unsigned long exit_qualification,
                                 u32 vmx_instruction_info, gva_t *ret)


-- 
Nadav Har'El                        |          Monday, Aug  2 2010, 22 Av 5770
nyh@math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Can Microsoft make a product that doesn't
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