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OvmfPkg/BaseMemEncryptSevLib: Maximize Page State Change efficiency 

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4654

When building the Page State Change entries for a range of memory, it can
happen that multiple calls to BuildPageStateBuffer() need to be made. If
the size of the input work area passed to BuildPageStateBuffer() exceeds
the number of entries that can be passed to the hypervisor using the GHCB
shared buffer, the Page State Change VMGEXIT support will issue multiple
VMGEXITs to process all entries in the buffer.

However, it could be that the final VMGEXIT for each round of Page State
Changes is only for a small number of entries and subsequent VMGEXITs may
still be issued to handle the full range of memory requested. To maximize
the number of entries processed during the Page State Change VMGEXIT,
limit BuildPageStateBuffer() to not build entries that exceed the maximum
number of entries that can be handled in a single Page State Change
VMGEXIT.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: Min Xu <min.m.xu@intel.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
This commit is contained in:
Tom Lendacky 2024-03-08 07:31:11 -08:00 committed by mergify[bot]
parent 2b330b57db
commit 069f9911a3
1 changed files with 11 additions and 0 deletions
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11
OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
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@ -145,6 +145,7 @@ BuildPageStateBuffer (
UINTN RmpPageSize;
UINTN Index;
UINTN IndexMax;
UINTN PscIndexMax;
// Clear the page state structure
SetMem (Info, InfoSize, 0);
@ -153,6 +154,16 @@ BuildPageStateBuffer (
IndexMax = (InfoSize - sizeof (Info->Header)) / sizeof (Info->Entry[0]);
NextAddress = EndAddress;
//
// Make the use of the work area as efficient as possible relative to
// exiting from the guest to the hypervisor. Maximize the number of entries
// that can be processed per exit.
//
PscIndexMax = (IndexMax / SNP_PAGE_STATE_MAX_ENTRY) * SNP_PAGE_STATE_MAX_ENTRY;
if (PscIndexMax > 0) {
IndexMax = MIN (IndexMax, PscIndexMax);
}
//
// Populate the page state entry structure
//