GHCI spec for TDX 1.0 says that the MapGPA call may fail with the R10
error code = TDG.VP.VMCALL_RETRY (1), and the guest must retry this
operation for the pages in the region starting at the GPA specified
in R11.
When a fully enlightened TDX guest runs on Hyper-V, Hyper-V can return
the retry error when set_memory_decrypted() is called to decrypt up to
1GB of swiotlb bounce buffers.
Acked-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Michael Kelley <[email protected]>
Signed-off-by: Dexuan Cui <[email protected]>
---
Changes in v2:
Used __tdx_hypercall() directly in tdx_map_gpa().
Added a max_retry_cnt of 1000.
Renamed a few variables, e.g., r11 -> map_fail_paddr.
Changes in v3:
Changed max_retry_cnt from 1000 to 3.
Changes in v4:
__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT) -> __tdx_hypercall_ret()
Added Kirill's Acked-by.
Changes in v5:
Added Michael's Reviewed-by.
Changes in v6: None.
Changes in v7:
Addressed Dave's comments:
see https://lwn.net/ml/linux-kernel/SA1PR21MB1335736123C2BCBBFD7460C3BF46A@SA1PR21MB1335.namprd21.prod.outlook.com
arch/x86/coco/tdx/tdx.c | 65 +++++++++++++++++++++++++++++++++--------
1 file changed, 53 insertions(+), 12 deletions(-)
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index cde174f4e239..5b62a1f5bd79 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -28,6 +28,8 @@
#define TDVMCALL_MAP_GPA 0x10001
#define TDVMCALL_REPORT_FATAL_ERROR 0x10003
+#define TDVMCALL_STATUS_RETRY 1
+
/* MMIO direction */
#define EPT_READ 0
#define EPT_WRITE 1
@@ -777,14 +779,16 @@ static bool try_accept_one(phys_addr_t *start, unsigned long len,
}
/*
- * Inform the VMM of the guest's intent for this physical page: shared with
- * the VMM or private to the guest. The VMM is expected to change its mapping
- * of the page in response.
+ * Notify the VMM about page mapping conversion. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface (GHCI),
+ * section "TDG.VP.VMCALL<MapGPA>".
*/
-static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
+static bool tdx_map_gpa(phys_addr_t start, phys_addr_t end, bool enc)
{
- phys_addr_t start = __pa(vaddr);
- phys_addr_t end = __pa(vaddr + numpages * PAGE_SIZE);
+ const int max_retries_per_page = 3;
+ struct tdx_hypercall_args args;
+ u64 map_fail_paddr, ret;
+ int retry_count = 0;
if (!enc) {
/* Set the shared (decrypted) bits: */
@@ -792,12 +796,49 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
end |= cc_mkdec(0);
}
- /*
- * Notify the VMM about page mapping conversion. More info about ABI
- * can be found in TDX Guest-Host-Communication Interface (GHCI),
- * section "TDG.VP.VMCALL<MapGPA>"
- */
- if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
+ while (retry_count < max_retries_per_page) {
+ memset(&args, 0, sizeof(args));
+ args.r10 = TDX_HYPERCALL_STANDARD;
+ args.r11 = TDVMCALL_MAP_GPA;
+ args.r12 = start;
+ args.r13 = end - start;
+
+ ret = __tdx_hypercall_ret(&args);
+ if (ret != TDVMCALL_STATUS_RETRY)
+ return !ret;
+ /*
+ * The guest must retry the operation for the pages in the
+ * region starting at the GPA specified in R11. R11 comes
+ * from the untrusted VMM. Sanity check it.
+ */
+ map_fail_paddr = args.r11;
+ if (map_fail_paddr < start || map_fail_paddr >= end)
+ return false;
+
+ /* "Consume" a retry without forward progress */
+ if (map_fail_paddr == start) {
+ retry_count++;
+ continue;
+ }
+
+ start = map_fail_paddr;
+ retry_count = 0;
+ }
+
+ return false;
+}
+
+/*
+ * Inform the VMM of the guest's intent for this physical page: shared with
+ * the VMM or private to the guest. The VMM is expected to change its mapping
+ * of the page in response.
+ */
+static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
+{
+ phys_addr_t start = __pa(vaddr);
+ phys_addr_t end = __pa(vaddr + numpages * PAGE_SIZE);
+
+ if (!tdx_map_gpa(start, end, enc))
return false;
/* private->shared conversion requires only MapGPA call */
--
2.25.1