Re: [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm: fix infinite loop issue in SMM profile

["Yao, Jiewen" <jiewen.yao@intel.com>]

Hi
May I know how "3" is calculated?

+  RestorePageNumber = 3;

Thank you
Yao Jiewen


> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Jian J
> Wang
> Sent: Tuesday, February 6, 2018 11:02 AM
> To: edk2-devel@lists.01.org
> Cc: Ni, Ruiyu <ruiyu.ni@intel.com>; Yao, Jiewen <jiewen.yao@intel.com>; Laszlo
> Ersek <lersek@redhat.com>; Dong, Eric <eric.dong@intel.com>
> Subject: [edk2] [PATCH] UefiCpuPkg/PiSmmCpuDxeSmm: fix infinite loop issue in
> SMM profile
> 
> The infinite loop is caused by the memory instruction, such as
> "rep mov", operating on memory block crossing boundary of NON-PRESENT
> pages. Because the address triggering page fault set in CR2 will be in
> the first page, SmmProfilePFHandler() will only change the first page
> into PRESENT. The page following will be still in NON-PRESENT status.
> 
> Since SmmProfilePFHandler() will setup single-step trap for the
> instruction causing #PF, when the handler returns back to the
> instruction and re-execute it, both #DB and #PF will be triggered
> because the instruction wants to access both first and second page
> but only first page is PRESENT.
> 
> Normally #DB exception will be handled first and its handler will
> change first page back to NON-PRESENT status. Then #PF is handled
> and its handler will change first page to PRESENT status again and
> setup another single-step for the instruction triggering #PF. Then
> the whole system falls into an infinite loop and the memory operation
> will never move on.
> 
> This patch fix above situation by always changing 3 pages to PRESENT
> status instead of just 1 page. Those 3 pages include the page before
> and after the page causing #PF because memory operation instruction
> may have direction flag (DF) set or cleared.
> 
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/SmmProfile.c | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/SmmProfile.c
> b/UefiCpuPkg/PiSmmCpuDxeSmm/SmmProfile.c
> index 9588eaf029..8cdfc82a92 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/SmmProfile.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/SmmProfile.c
> @@ -1302,6 +1302,8 @@ SmmProfilePFHandler (
>  {
>    UINT64                *PageTable;
>    UINT64                PFAddress;
> +  UINT64                RestoreAddress;
> +  UINTN                 RestorePageNumber;
>    UINTN                 CpuIndex;
>    UINTN                 Index;
>    UINT64                InstructionAddress;
> @@ -1331,10 +1333,22 @@ SmmProfilePFHandler (
>    PFAddress         = AsmReadCr2 ();
>    CpuIndex          = GetCpuIndex ();
> 
> -  if (PFAddress <= 0xFFFFFFFF) {
> -    RestorePageTableBelow4G (PageTable, PFAddress, CpuIndex, ErrorCode);
> -  } else {
> -    RestorePageTableAbove4G (PageTable, PFAddress, CpuIndex, ErrorCode,
> &IsValidPFAddress);
> +  //
> +  // Memory operation cross pages, like "rep mov" instruction, will cause
> +  // infinite loop between this and Debug Trap handler. Since the direction
> +  // of memory operation is unknown, the pages before and after current page
> +  // should be taken into account as well.
> +  //
> +  RestorePageNumber = 3;
> +  RestoreAddress = PFAddress - EFI_PAGE_SIZE;
> +  while (RestorePageNumber > 0) {
> +    if (RestoreAddress <= 0xFFFFFFFF) {
> +      RestorePageTableBelow4G (PageTable, RestoreAddress, CpuIndex,
> ErrorCode);
> +    } else {
> +      RestorePageTableAbove4G (PageTable, RestoreAddress, CpuIndex,
> ErrorCode, &IsValidPFAddress);
> +    }
> +    RestoreAddress += EFI_PAGE_SIZE;
> +    RestorePageNumber--;
>    }
> 
>    if (!IsValidPFAddress) {
> --
> 2.14.1.windows.1
> 
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