[RFC PATCH 4/6] x86/virt/tdx: Add SEAMCALL wrappers for TDX page cache management

Rick Edgecombe
2024-11-15T20:20:42Z

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>
---
SEAMCALL RFC:
- Use struct tdx_td
- Use arg names with meaning for tdh_phymem_page_reclaim() for out args

uAPI breakout v2:
- Change to use 'u64' as function parameter to prepare to move
SEAMCALL wrappers to arch/x86. (Kai)
- Split to separate patch
- Move SEAMCALL wrappers from KVM to x86 core;
- Move TDH_xx macros from KVM to x86 core;
- Re-write log

uAPI breakout v1:
- Make argument to C wrapper function struct kvm_tdx * or
struct vcpu_tdx * .(Sean)
- Drop unused helpers (Kai)
- Fix bisectability issues in headers (Kai)
- Updates from seamcall overhaul (Kai)

v19:
- Update the commit message to match the patch by Yuan
- Use seamcall() and seamcall_ret() by paolo

v18:
- removed stub functions for __seamcall{,_ret}()
- Added Reviewed-by Binbin
- Make tdx_seamcall() use struct tdx_module_args instead of taking
each inputs.
---
arch/x86/include/asm/tdx.h | 3 +++
arch/x86/virt/vmx/tdx/tdx.c | 38 +++++++++++++++++++++++++++++++++++++
arch/x86/virt/vmx/tdx/tdx.h | 3 +++
3 files changed, 44 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 83aa2a8a56d3..72de04dc242e 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -142,6 +142,9 @@ u64 tdh_mng_key_freeid(struct tdx_td *td);
u64 tdh_mng_init(struct tdx_td *td, u64 td_params, hpa_t *tdr);
u64 tdh_vp_init(struct tdx_vp *vp, u64 initial_rcx);
u64 tdh_vp_init_apicid(struct tdx_vp *vp, u64 initial_rcx, u32 x2apicid);
+u64 tdh_phymem_page_reclaim(hpa_t page, u64 *page_type, u64 *page_owner, u64 *page_size);
+u64 tdh_phymem_cache_wb(bool resume);
+u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td);
#else
static inline void tdx_init(void) { }
static inline int tdx_cpu_enable(void) { return -ENODEV; }
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index c125b1519072..6f833d816899 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1681,3 +1681,41 @@ u64 tdh_vp_init_apicid(struct tdx_vp *vp, u64 initial_rcx, u32 x2apicid)
return seamcall(TDH_VP_INIT | (1ULL << TDX_VERSION_SHIFT), &args);
}
EXPORT_SYMBOL_GPL(tdh_vp_init_apicid);
+
+u64 tdh_phymem_page_reclaim(hpa_t page, u64 *page_type, u64 *page_owner, u64 *page_size)
+{
+ struct tdx_module_args args = {
+ .rcx = page,
+ };
+ u64 ret;
+
+ ret = seamcall_ret(TDH_PHYMEM_PAGE_RECLAIM, &args);
+
+ *page_type = args.rcx;
+ *page_owner = args.rdx;
+ *page_size = args.r8;
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(tdh_phymem_page_reclaim);
+
+u64 tdh_phymem_cache_wb(bool resume)
+{
+ struct tdx_module_args args = {
+ .rcx = resume ? 1 : 0,
+ };
+
+ return seamcall(TDH_PHYMEM_CACHE_WB, &args);
+}
+EXPORT_SYMBOL_GPL(tdh_phymem_cache_wb);
+
+u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td)
+{
+ struct tdx_module_args args = {};
+
+ args.rcx = td->tdr | ((u64)tdx_global_keyid << boot_cpu_data.x86_phys_bits);
+
+ return seamcall(TDH_PHYMEM_PAGE_WBINVD, &args);
+}
+EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_tdr);
+
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index 3663971a3669..191bdd1e571d 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -26,11 +26,14 @@
#define TDH_MNG_INIT 21
#define TDH_VP_INIT 22
#define TDH_PHYMEM_PAGE_RDMD 24
+#define TDH_PHYMEM_PAGE_RECLAIM 28
#define TDH_SYS_KEY_CONFIG 31
#define TDH_SYS_INIT 33
#define TDH_SYS_RD 34
#define TDH_SYS_LP_INIT 35
#define TDH_SYS_TDMR_INIT 36
+#define TDH_PHYMEM_CACHE_WB 40
+#define TDH_PHYMEM_PAGE_WBINVD 41
#define TDH_SYS_CONFIG 45

/*
--
2.47.0