[v2,1/6] x86/tdx: Retry TDVMCALL_MAP_GPA() when needed
Commit Message
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 TDX guest runs on Hyper-V, Hyper-V returns the retry error
when hyperv_init() -> swiotlb_update_mem_attributes() ->
set_memory_decrypted() decrypts up to 1GB of swiotlb bounce buffers.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
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.
arch/x86/coco/tdx/tdx.c | 64 +++++++++++++++++++++++++++++++++--------
1 file changed, 52 insertions(+), 12 deletions(-)
Comments
On Tue, Dec 06, 2022 at 04:33:20PM -0800, Dexuan Cui wrote:
> 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 TDX guest runs on Hyper-V, Hyper-V returns the retry error
> when hyperv_init() -> swiotlb_update_mem_attributes() ->
> set_memory_decrypted() decrypts up to 1GB of swiotlb bounce buffers.
>
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
>
> 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.
>
> arch/x86/coco/tdx/tdx.c | 64 +++++++++++++++++++++++++++++++++--------
> 1 file changed, 52 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 3fee96931ff5..cdeda698d308 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -20,6 +20,8 @@
> /* TDX hypercall Leaf IDs */
> #define TDVMCALL_MAP_GPA 0x10001
>
> +#define TDVMCALL_STATUS_RETRY 1
> +
> /* MMIO direction */
> #define EPT_READ 0
> #define EPT_WRITE 1
> @@ -692,14 +694,15 @@ 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);
> + int max_retry_cnt = 1000, retry_cnt = 0;
Hm. max_retry_cnt looks too high to me. I expected to see 3 or something.
Any justification for it to be *that* high?
> From: Kirill A. Shutemov <kirill@shutemov.name>
> Sent: Thursday, December 8, 2022 11:48 AM
> To: Dexuan Cui <decui@microsoft.com>
> > [...]
> > +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);
> > + int max_retry_cnt = 1000, retry_cnt = 0;
>
> Hm. max_retry_cnt looks too high to me. I expected to see 3 or something.
>
> Any justification for it to be *that* high?
No. I just used an enough big number :-)
I'll change it to 3 in the next version.
@@ -20,6 +20,8 @@
/* TDX hypercall Leaf IDs */
#define TDVMCALL_MAP_GPA 0x10001
+#define TDVMCALL_STATUS_RETRY 1
+
/* MMIO direction */
#define EPT_READ 0
#define EPT_WRITE 1
@@ -692,14 +694,15 @@ 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);
+ int max_retry_cnt = 1000, retry_cnt = 0;
+ struct tdx_hypercall_args args;
+ u64 map_fail_paddr, ret;
if (!enc) {
/* Set the shared (decrypted) bits: */
@@ -707,12 +710,49 @@ 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 (1) {
+ 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(&args, TDX_HCALL_HAS_OUTPUT);
+ if (ret != TDVMCALL_STATUS_RETRY)
+ break;
+ /*
+ * The guest must retry the operation for the pages in the
+ * region starting at the GPA specified in R11. Make sure R11
+ * contains a sane value.
+ */
+ map_fail_paddr = args.r11;
+ if (map_fail_paddr < start || map_fail_paddr >= end)
+ return false;
+
+ if (map_fail_paddr == start) {
+ retry_cnt++;
+ if (retry_cnt > max_retry_cnt)
+ return false;
+ } else {
+ retry_cnt = 0;
+ start = map_fail_paddr;
+ }
+ }
+
+ return !ret;
+}
+
+/*
+ * 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 */