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Mon, 01 Apr 2019 10:01:39 -0700 (PDT) Sender: afish@apple.com From: Andrew Fish Message-id: <5345695C-14DF-4D3E-B8D8-30914252EF10@apple.com> Date: Mon, 01 Apr 2019 10:01:14 -0700 In-reply-to: Cc: nkvangup , edk2-devel , Yao Jiewen , Eric Dong To: Laszlo Ersek References: <20190401081601.22388-1-narendra.k.vanguput@intel.com> X-Mailer: Apple Mail (2.3445.6.18) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-04-01_05:, , signatures=0 X-Content-Filtered-By: Mailman/MimeDel 2.1.29 Subject: Re: [PATCH v9] UefiCpuPkg\CpuSmm: Save & restore CR2 on-demand paging in SMM X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 01 Apr 2019 17:01:46 -0000 Content-Type: text/plain; CHARSET=US-ASCII Content-Transfer-Encoding: 7BIT > On Apr 1, 2019, at 9:47 AM, Laszlo Ersek wrote: > > On 04/01/19 10:16, nkvangup wrote: >> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1593 >> >> For every SMI occurrence, save and restore CR2 register only when SMM >> on-demand paging support is enabled in 64 bit operation mode. >> This is not a bug but to have better improvement of code. >> >> Patch5 is updated with separate functions for Save and Restore of CR2 >> based on review feedback. >> >> Patch6 - Removed Global Cr2 instead used function parameter. >> >> Patch7 - Removed checking Cr2 with 0 as per feedback. >> >> Patch8 and 9 - Aligned with EDK2 Coding style. >> >> Contributed-under: TianoCore Contribution Agreement 1.1 >> Signed-off-by: Vanguput Narendra K >> Cc: Eric Dong >> Cc: Ray Ni >> Cc: Laszlo Ersek >> Cc: Yao Jiewen >> --- >> UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c | 26 ++++++++++++++++++++++++++ >> UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c | 9 ++++++--- >> UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h | 22 ++++++++++++++++++++++ >> UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c | 30 ++++++++++++++++++++++++++++++ >> 4 files changed, 84 insertions(+), 3 deletions(-) >> >> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c >> index b734a1ea8c..d1e146a70c 100644 >> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c >> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/Ia32/PageTbl.c >> @@ -316,3 +316,29 @@ SetPageTableAttributes ( >> >> return ; >> } >> + >> +/** >> + This function returns with no action for 32 bit. >> + >> + @param[out] *Cr2 Pointer to variable to hold CR2 register value. >> +**/ >> +VOID >> +SaveCr2 ( >> + OUT UINTN *Cr2 >> + ) >> +{ >> + return ; >> +} >> + >> +/** >> + This function returns with no action for 32 bit. >> + >> + @param[in] Cr2 Value to write into CR2 register. >> +**/ >> +VOID >> +RestoreCr2 ( >> + IN UINTN Cr2 >> + ) >> +{ >> + return ; >> +} >> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c >> index 3b0b3b52ac..ce70f77709 100644 >> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c >> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c >> @@ -1112,9 +1112,11 @@ SmiRendezvous ( >> ASSERT(CpuIndex < mMaxNumberOfCpus); >> >> // >> - // Save Cr2 because Page Fault exception in SMM may override its value >> + // Save Cr2 because Page Fault exception in SMM may override its value, >> + // when using on-demand paging for above 4G memory. >> // >> - Cr2 = AsmReadCr2 (); >> + Cr2 = 0; >> + SaveCr2 (&Cr2); >> >> // >> // Perform CPU specific entry hooks >> @@ -1253,10 +1255,11 @@ SmiRendezvous ( >> >> Exit: >> SmmCpuFeaturesRendezvousExit (CpuIndex); >> + >> // >> // Restore Cr2 >> // >> - AsmWriteCr2 (Cr2); >> + RestoreCr2 (Cr2); >> } >> >> /** >> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h >> index 84efb22981..38f9104117 100644 >> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h >> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h >> @@ -1243,4 +1243,26 @@ EFIAPI >> PiSmmCpuSmiEntryFixupAddress ( >> ); >> >> +/** >> + This function reads CR2 register when on-demand paging is enabled >> + for 64 bit and no action for 32 bit. >> + >> + @param[out] *Cr2 Pointer to variable to hold CR2 register value. >> +**/ >> +VOID >> +SaveCr2 ( >> + OUT UINTN *Cr2 >> + ); >> + >> +/** >> + This function writes into CR2 register when on-demand paging is enabled >> + for 64 bit and no action for 32 bit. >> + >> + @param[in] Cr2 Value to write into CR2 register. >> +**/ >> +VOID >> +RestoreCr2 ( >> + IN UINTN Cr2 >> + ); >> + >> #endif >> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c >> index 2c77cb47a4..95eaf0b016 100644 >> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c >> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/PageTbl.c >> @@ -1053,3 +1053,33 @@ SetPageTableAttributes ( >> >> return ; >> } >> + >> +/** >> + This function reads CR2 register when on-demand paging is enabled. >> + >> + @param[out] *Cr2 Pointer to variable to hold CR2 register value. >> +**/ >> +VOID >> +SaveCr2 ( >> + OUT UINTN *Cr2 >> + ) >> +{ >> + if (!mCpuSmmStaticPageTable) { >> + *Cr2 = AsmReadCr2 (); >> + } >> +} >> + >> +/** >> + This function restores CR2 register when on-demand paging is enabled. >> + >> + @param[in] Cr2 Value to write into CR2 register. >> +**/ >> +VOID >> +RestoreCr2 ( >> + IN UINTN Cr2 >> + ) >> +{ >> + if (!mCpuSmmStaticPageTable) { >> + AsmWriteCr2 (Cr2); >> + } >> +} >> > > I agree *how* this patch is implemented is correct, wrt. the IA32 / X64 > split. > > A slight improvement for edk2 coding style would be to replace "*Cr2" > with just "Cr2" in the @param[out] comments, but there's no need to > repost the patch just because of that. > > Regarding the "what" and "why", Nate's and Andrew's comments under v8 > make me uncomfortable about the patch. While the pre-patch comments do say > > Save Cr2 because Page Fault exception in SMM may override its value > > the post-patch comment (and code) are more restricted -- they claim that > such an exception (from which we return, anyway) may only occur when > on-demand paging is enabled (which is in turn a pre-requisite to both > the SMM profile feature and the SMM heap guard feature). > > It is this "narrowing" that concerns me (i.e. the claim that a page > fault that we consider "expected", and return from, may only occur due > to enabling on-demand paging). It *seems* like a correct statement, but > I'd like other reviewers to prove (or disprove) it; so I will not give > either A-b or R-b. > Laszlo, My understanding for SMM for X64 there are 2 options page tables from 0 - 4 GB + making page table entries on page faults, and a pure identity mapped page table. This behavior is controlled by a PCD setting. So that part of this patch makes sense to me. As I mentioned if the non SMM ring 0 CR2 is getting changed that seems like a bug to me. If the state save of CR2 is some internal state in SMM it feels like that should be better documented in the patch? Thanks, Andrew Fish > On the testing front, I confirm the patch doesn't regress OVMF. (OVMF > has on-demand paging *disabled* -- it uses static page tables in X64 SMM > --, so there the patch removes the CR2 save/restore, on both IA32 and X64.) > > Regression-tested-by: Laszlo Ersek > > > Thanks > Laszlo > _______________________________________________ > edk2-devel mailing list > edk2-devel@lists.01.org > https://lists.01.org/mailman/listinfo/edk2-devel