x86/virt/tdx: Add SEAMCALL wrappers for TDX page cache management

x86/virt/tdx: Add SEAMCALL wrappers for TDX page cache management

Intel TDX protects guest VMs from malicious host and certain physical
attacks. The TDX module uses pages provided by the host for both control
structures and for TD guest pages. These pages are encrypted using the
MK-TME encryption engine, with its special requirements around cache
invalidation. For its own security, the TDX module ensures pages are
flushed properly and track which usage they are currently assigned. For
creating and tearing down TD VMs and vCPUs KVM will need to use the
TDH.PHYMEM.PAGE.RECLAIM, TDH.PHYMEM.CACHE.WB, and TDH.PHYMEM.PAGE.WBINVD
SEAMCALLs.

Add tdh_phymem_page_reclaim() to enable KVM to call
TDH.PHYMEM.PAGE.RECLAIM to reclaim the page for use by the host kernel.
This effectively resets its state in the TDX module's page tracking
(PAMT), if the page is available to be reclaimed. This will be used by KVM
to reclaim the various types of pages owned by the TDX module. It will
have a small wrapper in KVM that retries in the case of a relevant error
code. Don't implement this wrapper in arch/x86 because KVM's solution
around retrying SEAMCALLs will be better located in a single place.

Add tdh_phymem_cache_wb() to enable KVM to call TDH.PHYMEM.CACHE.WB to do
a cache write back in a way that the TDX module can verify, before it
allows a KeyID to be freed. The KVM code will use this to have a small
wrapper that handles retries. Since the TDH.PHYMEM.CACHE.WB operation is
interruptible, have tdh_phymem_cache_wb() take a resume argument to pass
this info to the TDX module for restarts. It is worth noting that this
SEAMCALL uses a SEAM specific MSR to do the write back in sections. In
this way it does export some new functionality that affects CPU state.

Add tdh_phymem_page_wbinvd_tdr() to enable KVM to call
TDH.PHYMEM.PAGE.WBINVD to do a cache write back and invalidate of a TDR,
using the global KeyID. The underlying TDH.PHYMEM.PAGE.WBINVD SEAMCALL
requires the related KeyID to be encoded into the SEAMCALL args. Since the
global KeyID is not exposed to KVM, a dedicated wrapper is needed for TDR
focused TDH.PHYMEM.PAGE.WBINVD operations.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Message-ID: <20241203010317.827803-5-rick.p.edgecombe@intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>