Hi, > >>> Well, it's OVMF in a virtual machine. No boot guard involved. > >>> So we could probably go for a OVMF-specific patch here. > >>> > >>> But I'd prefer to figure what exactly is happening here before going > >>> down that route. An extreme slowdown just because we flip that bit > >>> doesn't make sense to me. > >>> > >>>> Why is boot time increasing? > >>> > >>> Not clear. It seems to be the lzma uncompress of the firmware volume > >>> in rom / pflash which is very slow. Also it is apparently only > >>> triggered in case pci device assignment is used. > >> > >> I've seen extreme slowness on physical platforms when we've mixed up the > >> MTRRs or page tables, causing code to be mapped uncached. > >> > >> Lzma uncompress of ROM could be pretty slow as well, if the ROM is being > >> read uncached. Lzma probably reads the data a byte at a time, which is the > >> worst case for uncached accesses. Since this is a VM, it's not actually > >> uncached at the hardware level, but I don't know how QEMU/KVM handles > >> uncached guest mappings.... It may be doing a VMEXIT for every byte. > >> > >> Anyway, I suggest double-checking your page tables and MTRRs. > > > > It happens very early at boot, before MTRRs are setup, running on the > > initial page tables created by the OVMF reset vector. The initial page > > tables have just 'accessed', 'dirty', 'read/write' and 'present' bits > > set for the 0-4G identity mapping. > > > > It seems to have something to do with EPT. It does not happen on AMD > > processors. It also does not happen when disabling EPT support in kvm > > on the host machine. > > > > looked at kvm kernel traces, I don't see excessive vmexits. > > This discussion evokes vague memories in me. I'll dump them here, but I > have no idea if they will be useful. (They probably won't.) > > - edk2 commit 98f378a7be12 ("OvmfPkg/ResetVector: enable caching in > initial page tables", 2013-09-24) > > - Linux (host) commit 879ae1880449 ("KVM: x86: obey > KVM_X86_QUIRK_CD_NW_CLEARED in kvm_set_cr0()", 2015-11-04)
I actually waded through the source code in both places ;) Turned out kvm propagates guest MTRR settings to EPT memory types, but only in case kvm_arch_has_noncoherent_dma() is true, which why this triggers only with a mdev device assigned. MTRR disabled gets translated to UNCACHABLE, this is where the slowdown comes from. Test patch below fixes it for me. take care, Gerd ----------------------------- cut here ---------------------------- commit eb9f40ffd8afad03ac1fb6ac0e2a9af12ae78152 Author: Gerd Hoffmann <kra...@redhat.com> Date: Tue Jan 23 15:33:51 2024 +0100 OvmfPkg/Sec: early mtrr setup Signed-off-by: Gerd Hoffmann <kra...@redhat.com> diff --git a/OvmfPkg/Library/PlatformInitLib/MemDetect.c b/OvmfPkg/Library/PlatformInitLib/MemDetect.c index f042517bb64a..14f39236e44d 100644 --- a/OvmfPkg/Library/PlatformInitLib/MemDetect.c +++ b/OvmfPkg/Library/PlatformInitLib/MemDetect.c @@ -1081,12 +1081,14 @@ PlatformQemuInitializeRam ( if (IsMtrrSupported () && (PlatformInfoHob->HostBridgeDevId != CLOUDHV_DEVICE_ID)) { MtrrGetAllMtrrs (&MtrrSettings); +#if 0 // // MTRRs disabled, fixed MTRRs disabled, default type is uncached // ASSERT ((MtrrSettings.MtrrDefType & BIT11) == 0); ASSERT ((MtrrSettings.MtrrDefType & BIT10) == 0); ASSERT ((MtrrSettings.MtrrDefType & 0xFF) == 0); +#endif // // flip default type to writeback diff --git a/OvmfPkg/Sec/SecMain.c b/OvmfPkg/Sec/SecMain.c index 9bd1b9c95227..2820be1bab7c 100644 --- a/OvmfPkg/Sec/SecMain.c +++ b/OvmfPkg/Sec/SecMain.c @@ -30,6 +30,7 @@ #include <Ppi/MpInitLibDep.h> #include <Library/TdxHelperLib.h> #include <Library/CcProbeLib.h> +#include <Register/Intel/ArchitecturalMsr.h> #include "AmdSev.h" #define SEC_IDT_ENTRY_COUNT 34 @@ -956,6 +957,19 @@ SecCoreStartupWithStack ( InitializeApicTimer (0, MAX_UINT32, TRUE, 5); DisableApicTimerInterrupt (); + // + // Early MTRR setup (enable + set sefault) + // + { + MSR_IA32_MTRR_DEF_TYPE_REGISTER DefType; + + DefType.Uint64 = 0; + DefType.Bits.Type = 6; /* write back */ + DefType.Bits.E = 1; /* enable */ + AsmWriteMsr64 (MSR_IA32_MTRR_DEF_TYPE, DefType.Uint64); + DEBUG ((DEBUG_ERROR, "%a:%d early mtrr: %lx\n", __func__, __LINE__, DefType.Uint64)); + } + // // Initialize Debug Agent to support source level debug in SEC/PEI phases before memory ready. // -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#114214): https://edk2.groups.io/g/devel/message/114214 Mute This Topic: https://groups.io/mt/100367559/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-