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3098e6eca8
Add support to allow guests to set the new CR3 control bits for Linear Address Masking (LAM) and add implementation to get untagged address for user pointers. LAM modifies the canonical check for 64-bit linear addresses, allowing software to use the masked/ignored address bits for metadata. Hardware masks off the metadata bits before using the linear addresses to access memory. LAM uses two new CR3 non-address bits, LAM_U48 (bit 62) and LAM_U57 (bit 61), to configure LAM for user pointers. LAM also changes VMENTER to allow both bits to be set in VMCS's HOST_CR3 and GUEST_CR3 for virtualization. When EPT is on, CR3 is not trapped by KVM and it's up to the guest to set any of the two LAM control bits. However, when EPT is off, the actual CR3 used by the guest is generated from the shadow MMU root which is different from the CR3 that is *set* by the guest, and KVM needs to manually apply any active control bits to VMCS's GUEST_CR3 based on the cached CR3 *seen* by the guest. KVM manually checks guest's CR3 to make sure it points to a valid guest physical address (i.e. to support smaller MAXPHYSADDR in the guest). Extend this check to allow the two LAM control bits to be set. After check, LAM bits of guest CR3 will be stripped off to extract guest physical address. In case of nested, for a guest which supports LAM, both VMCS12's HOST_CR3 and GUEST_CR3 are allowed to have the new LAM control bits set, i.e. when L0 enters L1 to emulate a VMEXIT from L2 to L1 or when L0 enters L2 directly. KVM also manually checks VMCS12's HOST_CR3 and GUEST_CR3 being valid physical address. Extend such check to allow the new LAM control bits too. Note, LAM doesn't have a global control bit to turn on/off LAM completely, but purely depends on hardware's CPUID to determine it can be enabled or not. That means, when EPT is on, even when KVM doesn't expose LAM to guest, the guest can still set LAM control bits in CR3 w/o causing problem. This is an unfortunate virtualization hole. KVM could choose to intercept CR3 in this case and inject fault but this would hurt performance when running a normal VM w/o LAM support. This is undesirable. Just choose to let the guest do such illegal thing as the worst case is guest being killed when KVM eventually find out such illegal behaviour and that the guest is misbehaving. Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Robert Hoo <robert.hu@linux.intel.com> Co-developed-by: Binbin Wu <binbin.wu@linux.intel.com> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com> Reviewed-by: Kai Huang <kai.huang@intel.com> Reviewed-by: Chao Gao <chao.gao@intel.com> Tested-by: Xuelian Guo <xuelian.guo@intel.com> Link: https://lore.kernel.org/r/20230913124227.12574-12-binbin.wu@linux.intel.com Signed-off-by: Sean Christopherson <seanjc@google.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.