On 5/30/2024 7:16 PM, Pankaj Gupta wrote:
From: Michael Roth <michael.roth@xxxxxxx>
Current SNP guest kernels will attempt to access these regions with
with C-bit set, so guest_memfd is needed to handle that. Otherwise,
kvm_convert_memory() will fail when the guest kernel tries to access it
and QEMU attempts to call KVM_SET_MEMORY_ATTRIBUTES to set these ranges
to private.
Whether guests should actually try to access ROM regions in this way (or
need to deal with legacy ROM regions at all), is a separate issue to be
addressed on kernel side, but current SNP guest kernels will exhibit
this behavior and so this handling is needed to allow QEMU to continue
running existing SNP guest kernels.
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
[pankaj: Added sev_snp_enabled() check]
Signed-off-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
---
hw/i386/pc.c | 14 ++++++++++----
hw/i386/pc_sysfw.c | 13 ++++++++++---
2 files changed, 20 insertions(+), 7 deletions(-)
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 7b638da7aa..62c25ea1e9 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -62,6 +62,7 @@
#include "hw/mem/memory-device.h"
#include "e820_memory_layout.h"
#include "trace.h"
+#include "sev.h"
#include CONFIG_DEVICES
#ifdef CONFIG_XEN_EMU
@@ -1022,10 +1023,15 @@ void pc_memory_init(PCMachineState *pcms,
pc_system_firmware_init(pcms, rom_memory);
option_rom_mr = g_malloc(sizeof(*option_rom_mr));
- memory_region_init_ram(option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE,
- &error_fatal);
- if (pcmc->pci_enabled) {
- memory_region_set_readonly(option_rom_mr, true);
+ if (sev_snp_enabled()) {
+ memory_region_init_ram_guest_memfd(option_rom_mr, NULL, "pc.rom",
+ PC_ROM_SIZE, &error_fatal);
+ } else {
+ memory_region_init_ram(option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE,
+ &error_fatal);
+ if (pcmc->pci_enabled) {
+ memory_region_set_readonly(option_rom_mr, true);
+ }
}
memory_region_add_subregion_overlap(rom_memory,
PC_ROM_MIN_VGA,
diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
index 00464afcb4..def77a442d 100644
--- a/hw/i386/pc_sysfw.c
+++ b/hw/i386/pc_sysfw.c
@@ -51,8 +51,13 @@ static void pc_isa_bios_init(MemoryRegion *isa_bios, MemoryRegion *rom_memory,
/* map the last 128KB of the BIOS in ISA space */
isa_bios_size = MIN(flash_size, 128 * KiB);
- memory_region_init_ram(isa_bios, NULL, "isa-bios", isa_bios_size,
- &error_fatal);
+ if (sev_snp_enabled()) {
+ memory_region_init_ram_guest_memfd(isa_bios, NULL, "isa-bios",
+ isa_bios_size, &error_fatal);
+ } else {
+ memory_region_init_ram(isa_bios, NULL, "isa-bios", isa_bios_size,
+ &error_fatal);
+ }
memory_region_add_subregion_overlap(rom_memory,
0x100000 - isa_bios_size,
isa_bios,
@@ -65,7 +70,9 @@ static void pc_isa_bios_init(MemoryRegion *isa_bios, MemoryRegion *rom_memory,
((uint8_t*)flash_ptr) + (flash_size - isa_bios_size),
isa_bios_size);
- memory_region_set_readonly(isa_bios, true);
+ if (!machine_require_guest_memfd(current_machine)) {
+ memory_region_set_readonly(isa_bios, true);
+ }
This patch takes different approach than next patch that this patch
chooses to not set readonly when require guest memfd while next patch
skips the whole isa_bios setup for -bios case. Why make different
handling for the two cases?
More importantly, with commit a44ea3fa7f2a,
pcmc->isa_bios_alias is default true for all new machine after 9.0, then
pc_isa_bios_init() would be hit even on plash case. It will call
x86_isa_bios_init() in pc_system_flash_map().
So with -bios case, the call site is
pc_system_firmware_init()
-> x86_bios_rom_init()
-> x86_isa_bios_init()
because require_guest_memfd is true for snp, x86_isa_bios_init() is
not called.
However, with pflash case, the call site is
pc_system_firmware_init()
-> pc_system_flash_map()
-> if (pcmc->isa_bios_alias) {
x86_isa_bios_init();
} else {
pc_isa_bios_init();
}
As I said above, pcmc->isa_bios_alias is true for machine after 9.0, so
it will goes x86_isa_bios_init().
So please anyone explain to me why x86_isa_bios_init() is ok for pflash
case but not for -bios case?
}
static PFlashCFI01 *pc_pflash_create(PCMachineState *pcms,
