Hi Ram, On Wed, Jul 18, 2012 at 1:31 AM, Ramshankar < [email protected]> wrote:
> On 17/07/12 00:17, Jaikumar G wrote: > >> Hi Ram, >> >> Thanks that makes a lot of sense. >> >> Regarding allocation of memory in guest space: >> >> "QEMU has a feature where it can translate a guest virtual address in >> user space directly into the corresponding physical/backing page in RAM >> without the need for allocating memory in Guest space." >> >> Is is something that can be done in virtual box ? Is there any >> significant performance differences ? >> >> > I don't know the context of that quote or what feature it refers to. As > far as VirtualBox is concerned, we could classify this into 2 cases for the > sake of simplicity. > > 1. Without Nested Paging (NP) / Extended Page Tables (EPT): the hypervisor > traps #PFs in the guest and syncs its shadow page tables. Host-side > translation of guest addresses is done by traversing the shadow page tables. > > 2. With NP/EPT: #PFs in the guest are handled without causing VM-exits as > the hardware supports an extra indirection of address translation. The host > TLBs can cache guest linear addresses to host physical addresses. > VirtualBox fully supports NP/EPT if the hardware has support for it. > Thanks for replying. Bare with me, as I am still trying to understand the memory mapping mechanism. The context of the question wast this. I was looking at PDMDevHlpPhysReadGCVirt - the destination pointer needs to be allocated for this. So I was looking for a function where I can avoid this allocation and the Guest Memory is direct mapped to Host and I get a pointer that I can use.. Thanks > Regards, > Ram. >
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